This a longstanding bug in mediawiki; it was originally filed
as bug 7304 [1]. The duplicate bug report 12791 [2] is easier
to understand. As that report says,
A page like
----
#REDIRECT [[bar]]
'''This''' is a [[foo]].
----
is shown as a redirect on foo's What links here.
- Carl
1:
https://bugzilla.wikimedia.org/show_bug.cgi?id=7304
2:
https://bugzilla.wikimedia.org/show_bug.cgi?id=12971