I have a set of rewrite rules (in a .htaccess) something like this:
RewriteRule ^list/vendor/(.*)$ list.php?vendor=$1 RewriteRule ^list/product/(.*)$ list.ph
Bah, I found it... Apache option AllowEncodedSlashes, which cannot be set per directory or from .htaccess, and which is Off by default.
Build-a-workaround time, if I can't get the hosting guys to turn it on in my virtual server.