I think that with those new elements Hofmator is right,
regexes aren't probably the good solution.

Especially with other simple answers available like :

print join'/',grep{if(!$u{$_}){$u{$_}=1}}split'/',$data;
[download]

Note to hofmator: don't hit me too hard...
My (poor) regex was not meant to be a solution but rather to show a possible way to study
(wasn't approach bold enough ? ;-)
Anyway I++ your post beccause your rightly outline some of the problems that may arise with the regex approach...
and in particular in my poor regex approach

"Only Bad Coders Code Badly In Perl" (OBC2BIP)