I can't seem to use parser functions of any sort inside the caret symbols... it just interprets things like {{#ucfirst:blah}} as plaintext. Am I missing something, or is this a bug?
Topic on Extension talk:CategorySortHeaders
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Oh, and I'm on MediaWiki 1.17, using the workaround described.
Ah, nevermind. I just realized that {{ucfirst}} doesn't use a "#" mark when being invoked. Anyways, great extension, thanks!