htaccess Detect Query then add Anchor tag - Sooo close

This SOMETIMES works - but under certain conditions I end up with the dreaded redirect loop. Scenario:

Use htaccess to look for a specific Query string, and if found, simply add a '#filter' to the end of the url and send it on its way.

RewriteCond %{QUERY_STRING} ^(.*)wpv_filter_submit=Apply(.*)$
RewriteRule ^(.*)$ /$1?%1&wpv_filter_submit=Apply&%2#filter [L,R=301,NE]

In some cases it actually works, others not. I think the problem is that there could be any number of query strings before or after this one and I'm not accounting for that properly?

It seems simple - just detect and add - but so far not the case.

Any thoughts greatly appreciated