Weston dropdown positioning bug

gistfile1.txt

Sometimes drop-down or contextual menus appear at the wrong position on the screen.
Upon moving the parent window, it appears that the menu position is not updated. They still appear at the same position.

To reproduce with affected applications, open app, open drop-down menu, move app window, open same drowpdown menu - observe that the menu has not moved with the window and is subsequently now appearing at a wrong position.
If the window is resized, the menus get re-aligned.

Weston 3.0.0
(running in DRM mode)

There is such a bug in sway too. But over there it seems to affect everything (pcmanfm, lxterminal, subl, chromium...)

Affected:
firefox
chromium (Contextual menu)
xnview
virtualbox
vlc 
(vlc, virtualbox and xnview have similar looking menus, I guess they use the same toolkit)
thunar

Not Affected:
lxterminal
weston-terminal
geeqie
pcmanfm (might be affected - drag and drop don't work)
lxmusic
inkscape
libreoffice
subl (Sublime Text 3)
Generally anything GNOME or LXDE

Dropdowns in PCManFM prefernces seems to work OK, but dropdowns in exo-preferred-applications are broken.
Yet these two look very similar, I think they use the same toolkit.