This logic error can cause clients to ignore host access control. http://lists.freedesktop.org/archives/xorg/2008-November/040235.html
Sorry, for some reason this commit didn't get into master: http://gitweb.freedesktop.org/?p=xorg/xserver.git;a=commit;h=3ec234976079d30f10e5246f6847a7eee01c144e It's fixed now...
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