What I do:
- search
- Spotweb
- click the glass (or choose category first, behavior is the same)
- do not enter anything
- hit the glass again so it will search

It looks like it fills a buffer for 50 articles orso. If the buffer needs to be filled again, it loads very old entries.
Interesting, this doesn't seem to happen on regular newznab indexers. Any chance you could PM me your Spot details so I could take a look at the results?