Mouse button actions all consumed by xfwm4 when using Xming or Cygwin/X
I believe it was moving from XFCE 4.12 to 4.14 that brought this about. When using Xming or Cygwin/X as the X server (on a separate machine running an old version of Windows), the XFCE desktop starts up and I can move the mouse pointer, but not click on anything or right-click to get any menus.
If I use the keyboard shortcuts to bring up a terminal, I can use the mouse normally to move and resize the window, but can't select any text in it or otherwise do anything by pressing the mouse buttons to affect it. Likewise other applications - their windows render correctly, but all the UI in them is unaffected by mouse clicks. The mouse wheel is similarly inhibited. (The keyboard works correctly.)
If I kill off xfwm4 (a number of times as it gets relaunched several times before it gives up) I am left with a desktop with no window manager (of course) but the terminal (last thing that had focus) now works correctly with the mouse and I can select text, copy/paste etc, scroll with the mouse wheel etc.
So it would appear that xfwm4 is consuming the mouse button presses (including the wheel), but only with Xming and Cygwin/X. I tried some other X servers (X-Win32, MobaXterm) and don't see the issue with those (the mouse works). Unfortunately, Xming and Cygwin/X have an (unrelated) feature I find particularly useful in my setup. The misbehaviour also indicates something unintended might be happening.
My Linux system is Gentoo (default 17.1 profile, not desktop or hardened etc.), and I've tried both xfwm4-4.14.2 and xfwm4-4.15.1 with the same result.