Comment 26 for bug 437378

well you're more familiar with the dark side of X than me ^^
anyway it's not yet "my fault" ;-)
doing furher investigation, I've found that the colormap is set when I call the function gdk_x11_gl_config_new_from_visualid (which gets an opengl config from an ARGB visual, which is then used to give opengl abilities to the GTK windows of the dock).
I'm going to dig into gdkgl to see if I can undestand why it happens.

I still don't see why this should be a problem for Qt apps though (although I do agree that it sounds weird to change the root colormap).

thanks again for your help !