Since bug 868255 is closed, please keep this bug open until upstream will hopefully eventually get rid of x11-libs/gtkglext, so we can track the issue and have a valid blocker. Also if anyone finds a way to raise the issue with upstream, feel free.
Could have re-opened the old one, that's the third one we have now...
Ok, I'll reopen that one and mark this as duplicate.
*** This bug has been marked as a duplicate of bug 868255 ***