When <categorytree>Foo</categorytree> is called on an non-existent category Foo, all strip markers before the tag are left stripped (see URL). Probably, there's a recursive call to the parser inside the extension which clears the parser state.
Version: unspecified
Severity: normal
URL: http://en.wikipedia.org/w/index.php?title=Wikipedia:WikiProject_Climbing&oldid=254590422