According to [1] the problem is with Tk 8.4. Googling also suggests this.
Tk bugtracker has no records mentioning XCB, libxcb or the "xcb_xlib_lock" function though.
1. http://lists.debian.org/debian-devel-announce/2006/11/msg00010.html -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
