While domains are case-insensitive (as described), the path isn't. If you browse to http://en.wikipedia.org/WIKI/, it doesn't work because the path after the domain _is_ case sensitive. Special:LinkSearch works according to this.

Now, should the path become case-insensitive for searching purposes? Probably, it'd be helpful. Is it broken? No.

The strange thing is, if I point my browser to http://ufbir.ifas.ufl.edu/cHaP21.htm it *does* work... maybe it depends on the server's OS? Indeed, IIRC on Windows the capitalization of paths is irrelevant while on Linux it isn't... right? Anyway, as you say, LinkSearch could be improved if all queries were lowercased first.

Paths are opaque, and must be assumed to be case-sensitive. (They are when pointing at a standard Unix filesystem; may not be for Windows or Mac filesystems, and all bets are off if they're interpreted by a script of any kind, which there's no way to tell if it will happen.)

For sorting/searching purposes, it probably wouldn't hurt to do indexing with case-folding, though. This would require a tweak to the URL indexing function, then updates to existing records in externallinks table.

Extensions is now part of MediaWiki core (1.14alpha) -> changing product and component