Did some quick testing. This also exhibits the same behavior on my system:
Screen 0 "Screen0" 0 0 Screen 1 "Screen1" Above "Screen0"
or
Screen 1 "Screen1" 0 0 Screen 0 "Screen0" Below "Screen1"
Disabling Xinerama removes the symptoms.
Did some quick testing. This also exhibits the same behavior on my system:
Screen 0 "Screen0" 0 0
Screen 1 "Screen1" Above "Screen0"
or
Screen 1 "Screen1" 0 0
Screen 0 "Screen0" Below "Screen1"
Disabling Xinerama removes the symptoms.