Stanislaw, thank you for the bug report!
you mention aiglx on your last comment. By any chance, have you installed aiglx or Xgl from external repositories? External aiglx/Xgl repositories are known to be unstable on Dapper, and are not supported. -- Fast scrolling causes X hang https://launchpad.net/bugs/47542 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
