I've never had much luck getting the keyword Agenda view to work correctly: there was a mention here before about Agenda file/buffer restrictions piling up over time, not getting cleared, but I don't actually use such restrictions much, and I still have the problem.
It seems like the longer I've had Emacs/Org up and running, the less the keyword Agenda search can find. The regexp search always works correctly, but the keyword search just finds progressively fewer and fewer entries. I haven't yet been able to see a pattern, but restarting Emacs fixes it -- I can find everything again. Has anyone seen this before? I'll go code diving in a few days, but if anyone has any insights in the meantime, please let me know... Eric