You can see this in any WM. (but the "error" happens in awesome and i3)
The most common widget to test are sub-submenus, like the ones in JuceDemoHost.
They will take the focus out of the parent window, because the sub-submenu is a window itself.
On tiling WMs this will cause the submenu to appear in a new screen area/section or even on a different screen...
The patch I posted fixes some other things too.
The fist part:
if (! comp->isOnDesktop())
Is because the juce code seems wrong. Why would it check if it was on desktop then add it again?
Whoever wrote the code probably mis-added the "!".
The last part:
Is needed to make a plugin I have work correctly.
Without the temporary flag juce will create a regular x11 window for it, which skips the fix this patch is all about.
I think there are other parts of the code that also need this extra flag (the submenus?),
but I'm waiting for this initial patch to be accepted before digging any deeper.