After some digging, I found that the xlib-xcb USE flag breaks some packages, like libreoffice (in impress it causes presentations not to be shown when hardware acceleration is on) and virt-manager (remote console display does not work). Looking at portage, I spotted only some warnings saying to enable this flag if something goes wrong with gtk+ or nx, or something like that. Due to the fact that this use flag can cause subtle bugs, difficult to track down (a google and this bugtracker can show some of them), wouldn'it be better to place at least a warning in ebuild, stating that some packages can be hindered by the xlib-xcb use flag? what do you think? Reproducible: Always
*** This bug has been marked as a duplicate of bug 441878 ***