As I've mentioned before, I'm pretty sure it's the encoding hack I set up to keep ampersands in titles _in_ the titles instead of as raw ampersands that indicate the beginning of the next variable in the query string:
RewriteEngine On RewriteMap urlencode prg:/usr/local/bin/urlencode RewriteRule ^/wiki/(.*)$ /w/wiki.phtml?title=${urlencode:$1} [L]If the hackish little external program should die or get out of sync, we end up with the wrong URLs. But this ugliness *shouldn't* be needed. We *should* be able to use the internal function that Apache provides for this...
You are mistaken that Apache is doing the wrong thing: ampersands are /not/ supposed to be urlencoded--they are valid and meaningful characters needed for URLs. But ampersands do need to be messed with for Wikipedia-specific reasons: since article titles must appear as values in the query string (which is separated by ampersands), they must be escaped somehow for that function. Also, the non-escaped ampersands in the URL must be HTML-escaped when they appear as attribute values, such as HREFs. These are both entirely separate issues, and the code formerly dealt with them correctly, although in a way that you didn't like. We may have to compromise; accept the double-encoding for ampersands that you removed for other characters. Either that, or come up with some other escaping mechanism for ampersands in titles.