GNOME Bugzilla – Bug 129919
Places some non-GTK2 Dialogs between Xinerama Screens
Last modified: 2004-12-22 21:47:04 UTC
This bug was originally reported in the Debian BTS: http://bugs.debian.org/220771 "Metacity places dialogs/windows of GTK 1.2 apps (e.g. unison-gtk, easytag) exactly centered on the Display, in my case exactly between my two equally-sized Xinerama screens."
metacity doesn't place those dialogs; these are windows that have either the PPosition or USPosition hints set. Unfortunately, there's really not anything metacity can do to fix this, since we've found that not honoring these hints causes a good many applications, such as java and other proprietary toolkits, to break.
If the answer isn't clear, the problem is that the app specifies/forces the position overlapping two screens. So you need to file bugs vs. these apps.