The PingLimiter hooks allows extensions to override throttles for a user. If you look at the docs (http://www.mediawiki.org/wiki/Manual:Hooks/PingLimiter), you'll see the third parameter (the output result of the ping limiting) is a reference. This makes sense.

However, if you look at the code, it's actually not passed as a reference, which means extensions are quite literally passed a useless parameter that is set to false always.

Version: unspecified
Severity: normal
URL: http://www.mediawiki.org/wiki/Manual:Hooks/PingLimiter