I think this might be another problem. Context menu searcher uses strictly hashes, that means, if you can not find subtitles using menu searcher, it means, hash doesnt exists.
On website you are 99% looking for movie name, so you get some results, which are OK, but not 100%.
Anyway, this is old story - if you find some GOOD subtitles, just upload them back with your movie (hash), so in future you can find this movie using context menu and you will help others like you.
read here more
http://trac.opensubtitles.org/projects/opensubtitles