Expert advice needed on problems with oxygen + alpha channel

[Hugo Pereira Da Costa]

Hello,

I'm facing a bug with oxygen and KToolBar when compositing is active 
that I need expert advice on.

The issue: when you detach (unlock and move out of the window) a 
KToolbar from a main window, oxygen gives it the "translucent 
background" flag, and uses it to draw nice beveled corner on the 
detached toolbar. The same *was* done for Dockwidgets, and it *used to* 
work in both cases.

Sadly enough it does not work anymore (try it with e.g. toolbars in 
dolphin). You get a zillion of errors message like:

X Error: BadMatch (invalid parameter attributes) 8
   Major opcode: 62 (X_CopyArea)
   Resource id:  0x22027d8

and the toolbar contents is not drawn anymore.

Nor does it work for Dockwidgets in which there is a KPart (okular or 
kate), as was reported in bug https://bugs.kde.org/show_bug.cgi?id=273848

To fix the bug, I found a workaround that unfortunately looks nice only 
when using KWin. I could do the same for KToolBars, but what annoys me is

- it does work without the workaround for other QDockWidgets (with no 
kpart in there)
- it does work without the workaround for QToolBar (try, e.g. in QGit, 
or Quassel)
- it looks ugly when using kde applications in another DE.

I believe it is somehow related to XmlGui, and would rather have this 
fixed there, than propagating ugly workarounds. However, I have no clue 
where to look, how to start.

Advice ?

Thanks in advance,

Hugo