After performing an advanced search in the opac, if you click on the link to return to the last Advanced Search it is incorrectly encoded and results in a 404 page error. Changing line 117 of opac-results.tt from <p><a href="[% ReturnPath | uri %]">Return to the last advanced search</a></p> to <p><a href="[% ReturnPath | $raw %]">Return to the last advanced search</a></p> corrects the problem.
It's now: <p><a href="[% ReturnPath | url %] This seems to work well in my tests. Marking "WORKSFORME".