Multiple values for one permission pair handled wrong

While installing/uninstalling extensions I auto merged XWikiPreferences page and some strange state occured in my XWiki instance.

XWikiPreferences contains 2 objects of type XWikiGlobalRights now with same permission pair (XWikiGuest - register) but different values (see screenshot).

With such state wrong (imho) XWiki behavior occured:

1. Permission editor shows second permission (disabled), but first permission (enabled) used while accessing registration page (so unregistered users may register).
2. Modification of "register" permission of guest user in Permissions editor do nothing (checkbox is changing but duplicated "enabled" value is never cleared).

As I think behavior should be:
1. If different values for one permission pair (User/Group - Permission) is in place - "disabled" value must take precedence)
2. Permission editor should remove duplicates when changing permission value.