Comment # 7 on bug 1043221 from Fabian Vogt

I'm afraid I have to reopen this.

The fix for this bug causes breakage when the system's hostname changed during
an active X session.
Normally that should be fixed by the $XAUTHLOCALHOSTNAME envar, but if
.Xauthority contains a MIT-MAGIC-COOKIE-1 for the display with the new hostname
(from a previous session, for instance), libxcb does not try to fallback to
$XAUTHLOCALHOSTNAME. That behaviour is also obvious while reading the libxcb
patch that implements it and I attempted fixing it:
https://build.opensuse.org/package/rdiff/home:favogt:branches:X11:XOrg/libxcb?opackage=libxcb&oproject=X11%3AXOrg&rev=5

However, the fix breaks some X sessions completely, I'm not sure why yet and I
don't plan on debugging this further myself, as I don't really know what's
going on inside libxcb.

My question is: What is the correct/expected behaviour of a DM when starting a
session? Is it supposed to clear all cookies, only some of them or just add the
current display's cookies?

Reassigning to XOrg maintainers as the bug in libxcb should be fixed in either
case.