See https://meta.wikimedia.org/w/index.php?title=Special%3ALog&type=gblrights&user=MF-Warburg&page=Special%3AWikiSets%2F12&year=&month=-1&tagfilter=
I have just wanted to change it and it complained that the wiki pa_uswikimedia does not exist, so I simply removed it. Trying to readd does not work, even though it still appears in the list of wikis /not/ contained in the set.
Probably related to the rename described in bug 19986 comment 12.
Version: unspecified
Severity: trivial
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=58024