Xfce4-panel doesn't react properly on changes made by xfconf-query

Submitted by drkwv

Link to original bug (#12355)

Description

$ xfce4-panel --version
xfce4-panel 4.11.0 (Xfce 4.10)

I have run into the problem while writing a script that sets up my personal xfce4 settings using command line interface. I was unable to add applicationsmenu plugin onto panel even after restarting xfce4-panel with xfce4-panel --quit. It worked only after OS reboot (which was a preferrable alternative to session logout in my case).

Way to reproduce the bug:

1. Reset all "xfce4-panel" values with "xfconf-query".
2. Reboot the system.
3. Login into desktop with free floating empty panel.
4. Execute next xfconf queries:

xfconf-query --create --channel 'xfce4-panel' --property '/configver' --type 'int' --set '2'
xfconf-query --create --channel 'xfce4-panel' --property '/panels' --type 'int' --set '1'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/autohide' --type 'bool' --set 'false'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/background-alpha' --type 'int' --set '100'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/background-style' --type 'int' --set '0'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/enter-opacity' --type 'int' --set '100'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/leave-opacity' --type 'int' --set '100'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/length' --type 'int' --set '100'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/length-adjust' --type 'bool' --set 'true'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/mode' --type 'int' --set '0'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/position' --type 'string' --set 'p=6;x=0;y=0'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/position-locked' --type 'bool' --set 'true'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/size' --type 'int' --set '48'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/span-monitors' --type 'bool' --set 'false'
xfconf-query --create --channel 'xfce4-panel' --property '/panels/panel-1/plugin-ids' --force-array --type 'int' --set '1'
xfconf-query --create --channel 'xfce4-panel' --property '/plugins/plugin-1' --type 'string' --set 'applicationsmenu'

5. Applicationsmenu button would not show until you reboot or add it manually through the GUI. It will not show even if you reload the xfce4-panel although there would be no difference in xfce4-settings-editor between the settings you put through xfconf-query or between the settings you'll made through the panel settings GUI.
6. There is probability that xfce4-panel -s would take settings from a unknown different place and write it to ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml disregards of what you have entered using xfconf-query.

Version: 4.12.0