This is a known limitation of many conditional value lists. When you enter find mode, that blank "request" record that pops up seems to keep the relationship and/or calculations needed to produce the list from working.
One work around is to set up some global fields with your conditional value lists. The user can select the criteria in these fields while in browse mode then click a "find" button to perform a script that uses the data in the global fields to perform your find.
I have come across this same issue in FM Pro 12, and am wondering if now (July 2015) four years after this post was first answered, there might be some easier resolution put forth by Filemaker? Thank you.
I was experiencing a similar situation as noted in the original post (a conditional value list that worked in browse mode, but not in find mode). The same <no values defined> was displayed. In my case, I was filtering the value list to limit it to active records only and was using a calculated field (i.e. the entry "active" was made in the field using a calculation) that was unstored. The issue was resolved, in my case, by changing the storage options for the calculated field to "Use global storage (one value for all records)".