In 0.5.5 I enabled multiselect for the issue status in
issue.search
(<select name="status" multiple>) and one of my custom
multilink properties.

This triggered a problem in cgi/client.py:searchAction():
   if not self.form[key].value: continue
in line 937 fails because the form[key] then is a list of 
FieldStorages, not a FieldStorage itself. Attached is a
patch for 
this problem which works fine for me.