xfce4-panel segfaults with labwc ext-workspaces (on master branch)

When trying to run xfce4-panel 4.20.0 from Arch Linux repos on labwc 0.8.2 master (--EDITED--) I get the following:

--EDITED-- See next post for breaking labwc-commit.

johan@arch3 ~ % xfce4-panel 

(xfce4-panel:4010): GLib-GObject-CRITICAL **: 16:08:36.357: g_object_new_is_valid_property: object class 'XfwWorkspaceGroupWayland' has no property named 'handle'
[1]    4010 segmentation fault (core dumped)  xfce4-panel

Have removed ~/.config/xfce4/ and ~/.cache/ to rule out an old settings triggering the problem.

With gdb I get the following backtrace:

run:

xfce4-panel-Message: 15:46:29.078: Forcing all plugins to run internal                                                        

(xfce4-panel:2126): GLib-GObject-CRITICAL **: 15:46:29.082: g_object_new_is_valid_property: object class 'XfwWorkspaceGroupWayland' has no property named 'handle'

Thread 1 "xfce4-panel" received signal SIGSEGV, Segmentation fault.

Downloading 71.61 K source file /usr/src/debug/wayland/build/../wayland-1.23.1/src/wayland-client.c

0x00007ffff7f759c8 in wl_proxy_add_listener (proxy=0x0, implementation=0x7ffff7d9ae40 <group_listener>, data=0x555555726ea0)  
    at ../wayland-1.23.1/src/wayland-client.c:649
649		if (proxy->flags & WL_PROXY_FLAG_WRAPPER)

bt:

#0  0x00007ffff7f759c8 in wl_proxy_add_listener (proxy=0x0, 
    implementation=0x7ffff7d9ae40 <group_listener>, data=0x555555726ea0)
    at ../wayland-1.23.1/src/wayland-client.c:649
#1  0x00007ffff70bd97a in g_object_new_internal (class=0x55555573d7a0, 
    params=0x7fffffffc610, n_params=2) at ../glib/gobject/gobject.c:2657
#2  0x00007ffff70bfafb in g_object_new_internal (class=0x55555573d7a0, 
    params=0x7fffffffc610, n_params=2) at ../glib/gobject/gobject.c:2923
#3  g_object_new_valist (object_type=<optimized out>, 
    first_property_name=first_property_name@entry=0x7ffff7d8d71f "screen", 
    var_args=var_args@entry=0x7fffffffc8e0) at ../glib/gobject/gobject.c:2945
#4  0x00007ffff70bfeb0 in g_object_new (object_type=<optimized out>, 
    first_property_name=first_property_name@entry=0x7ffff7d8d71f "screen")
    at ../glib/gobject/gobject.c:2418
#5  0x00007ffff7d8c8de in manager_workspace_group (data=0x55555568c270, 
    manager=<optimized out>, wl_group=0x555555756270)
    at /usr/src/debug/libxfce4windowing/libxfce4windowing/libxfce4windowing/xfw-workspace-manager-wayland.c:186
#6  0x00007ffff6b02596 in ffi_call_unix64 () at ../src/x86/unix64.S:104
#7  0x00007ffff6aff00e in ffi_call_int (cif=cif@entry=0x7fffffffcbb0, 
    fn=<optimized out>, rvalue=<optimized out>, avalue=<optimized out>, 
    closure=closure@entry=0x0) at ../src/x86/ffi64.c:673
#8  0x00007ffff6b01bd3 in ffi_call (cif=cif@entry=0x7fffffffcbb0, 
    fn=<optimized out>, rvalue=rvalue@entry=0x0, 
    avalue=avalue@entry=0x7fffffffcc80) at ../src/x86/ffi64.c:710
#9  0x00007ffff7f758b0 in wl_closure_invoke (closure=closure@entry=0x5555556a62b0, 
    target=<optimized out>, target@entry=0x555555745790, opcode=opcode@entry=0, 
    data=<optimized out>, flags=1) at ../wayland-1.23.1/src/connection.c:1228
#10 0x00007ffff7f76139 in dispatch_event (display=display@entry=0x5555555d5f10, 
    queue=queue@entry=0x5555555d6008)
    at ../wayland-1.23.1/src/wayland-client.c:1674
#11 0x00007ffff7f76553 in dispatch_queue (display=0x5555555d5f10, 
    queue=0x5555555d6008) at ../wayland-1.23.1/src/wayland-client.c:1820
#12 wl_display_dispatch_queue_pending (display=0x5555555d5f10, 
    queue=0x5555555d6008) at ../wayland-1.23.1/src/wayland-client.c:2062
#13 0x00007ffff7f781c4 in wl_display_dispatch_queue (display=<optimized out>, 
    queue=<optimized out>) at ../wayland-1.23.1/src/wayland-client.c:2038
#14 0x00007ffff7f781e1 in wl_display_dispatch (display=<optimized out>)
    at ../wayland-1.23.1/src/wayland-client.c:2105
#15 0x00007ffff7d8847a in xfw_screen_wayland_constructed (obj=0x5555556e68c0)
    at /usr/src/debug/libxfce4windowing/libxfce4windowing/libxfce4windowing/xfw-screen-wayland.c:136
#16 0x00007ffff70bd97a in g_object_new_internal (class=0x5555556a83a0, 
    params=0x7fffffffcff0, n_params=1) at ../glib/gobject/gobject.c:2657
#17 0x00007ffff70bfafb in g_object_new_internal (class=0x5555556a83a0, 
    params=0x7fffffffcff0, n_params=1) at ../glib/gobject/gobject.c:2923
#18 g_object_new_valist (object_type=<optimized out>, 
    first_property_name=first_property_name@entry=0x7ffff7d8d71b "gdk-screen", 
    var_args=var_args@entry=0x7fffffffd2c0) at ../glib/gobject/gobject.c:2945
#19 0x00007ffff70bfeb0 in g_object_new (object_type=<optimized out>, 
    first_property_name=first_property_name@entry=0x7ffff7d8d71b "gdk-screen")
    at ../glib/gobject/gobject.c:2418
#20 0x00007ffff7d7d06c in xfw_screen_get (gdk_screen=0x5555555dd5a0)
    at /usr/src/debug/libxfce4windowing/libxfce4windowing/libxfce4windowing/xfw-screen.c:593
#21 IA__xfw_screen_get_default ()
    at /usr/src/debug/libxfce4windowing/libxfce4windowing/libxfce4windowing/xfw-screen.c:623
#22 0x000055555558a675 in panel_window_screen_changed (
    widget=widget@entry=0x55555573cfc0, previous_screen=previous_screen@entry=0x0)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/panel-window.c:1957
#23 0x000055555558a82f in panel_window_init (window=0x55555573cfc0)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/panel-window.c:698
#24 0x00007ffff70d8b09 in g_type_create_instance (type=<optimized out>)
    at ../glib/gobject/gtype.c:1951
#25 0x00007ffff70bd805 in g_object_new_internal (class=0x555555626b80, 
    params=0x7fffffffd6a0, n_params=9) at ../glib/gobject/gobject.c:2606
#26 0x00007ffff70bfafb in g_object_new_internal (class=0x555555626b80, 
    params=0x7fffffffd6a0, n_params=9) at ../glib/gobject/gobject.c:2923
#27 g_object_new_valist (object_type=<optimized out>, 
    first_property_name=first_property_name@entry=0x555555590d4e "id", 
    var_args=var_args@entry=0x7fffffffd970) at ../glib/gobject/gobject.c:2945
#28 0x00007ffff70bfeb0 in g_object_new (object_type=<optimized out>, 
    first_property_name=first_property_name@entry=0x555555590d4e "id")
    at ../glib/gobject/gobject.c:2418
#29 0x0000555555586afa in panel_window_new (screen=0x5555555dd5a0, id=1, 
    autohide_block=0)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/panel-window.c:4002
#30 0x00005555555719ac in panel_application_new_window (
    application=application@entry=0x55555570b0c0, screen=screen@entry=0x0, panel_id=panel_id@entry=1, new_window=new_window@entry=0)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/panel-application.c:1568
#31 0x0000555555571d24 in panel_application_load_real (application=application@entry=0x55555570b0c0)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/panel-application.c:448
#32 0x0000555555572188 in panel_application_load (application=0x55555570b0c0, disable_wm_check=<optimized out>)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/panel-application.c:1291
#33 0x0000555555572324 in panel_dbus_name_acquired (connection=<optimized out>, name=<optimized out>, user_data=<optimized out>)
    at /usr/src/debug/xfce4-panel/xfce4-panel/panel/main.c:208
#34 0x00007ffff7203b4d in actually_do_call (client=0x555555750040, connection=<optimized out>, call_type=CALL_TYPE_NAME_ACQUIRED) at ../glib/gio/gdbusnameowning.c:153
#35 do_call (client=0x555555750040, call_type=CALL_TYPE_NAME_ACQUIRED) at ../glib/gio/gdbusnameowning.c:205
#36 0x00007ffff7203d7a in call_acquired_handler (client=0x555555750040) at ../glib/gio/gdbusnameowning.c:219
#37 call_acquired_handler (client=0x555555750040) at ../glib/gio/gdbusnameowning.c:210
#38 on_name_lost_or_acquired (connection=<optimized out>, sender_name=<optimized out>, object_path=<optimized out>, interface_name=<optimized out>, 
    signal_name=0x7fffdc002810 "NameAcquired", parameters=0x7fffdc003fd0, user_data=0x555555750040) at ../glib/gio/gdbusnameowning.c:286
#39 on_name_lost_or_acquired (connection=<optimized out>, sender_name=0x7fffdc006b50 "org.freedesktop.DBus", object_path=<optimized out>, 
    interface_name=<optimized out>, signal_name=0x7fffdc002810 "NameAcquired", parameters=0x7fffdc003fd0, user_data=0x555555750040) at ../glib/gio/gdbusnameowning.c:250
#40 0x00007ffff71fb9b9 in emit_signal_instance_in_idle_cb (data=0x7fffdc003790) at ../glib/gio/gdbusconnection.c:4189
#41 0x00007ffff6fa7559 in g_main_dispatch (context=0x5555555e8cc0) at ../glib/glib/gmain.c:3357
#42 0x00007ffff700a257 in g_main_context_dispatch_unlocked (context=0x5555555e8cc0) at ../glib/glib/gmain.c:4208
#43 g_main_context_iterate_unlocked.isra.0 (context=0x5555555e8cc0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/glib/gmain.c:4273
#44 0x00007ffff6fa8287 in g_main_loop_run (loop=0x555555743080) at ../glib/glib/gmain.c:4475
#45 0x00007ffff75e4ebf in gtk_main () at ../gtk/gtk/gtkmain.c:1329
#46 0x0000555555566440 in main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/xfce4-panel/xfce4-panel/panel/main.c:378