There's just a bit of chaos being caused due to the fact that MW considers page names that end with "/" to be valid targets. The following rule prevents people from going onto a page that ends with a "/", but not prevent people from getting to current pages via "/#" so they can fix them.
This mod_rewrite rule will fix it:
RewriteRule ^(.*)/$ $1 [R=301]
Alternately, this mod_alias rule '''may''' fix it:
RedirectMatch permanent (.*)/ $1
I suppose it might be useful to have this rewritten to Special:Prefixindex so that you get a kind of "directory listing," but that's probably overkill. I think the rewrite is a good idea in any case.
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