Since a couple of weeks every time I create a new Chromium window it is
completely invisible until I minimize and restore it. What I see instead of the
new Chrome window is the underlying one.
Without compositing it works flawlessly (my desktop environment is KDE 4.14.3
so the compositor is KWin).

Graphic stack is from git (including xorg, llvm, mesa and drm-next-3.20).

I am sure the regression isn't in the kernel, maybe it is due to Chromium 40
exposing it (I don't remember having it with v39) but I'm not sure.