wordpress search and comments are not returning correct results

hi again, I noticed this problem in conjunction with the one I’d posted earlier that still isn’t resolved:

http://wordpress.org/support/topic/69248?replies=6

when I search a string under Manage and Posts, I get different results every time and never as many results as there actually are. I was trying to track down the number of posts that link to my old movable type archive structure (http://mixvio.com/ar/*) and I know for a fact there are over a hundred entries with that string, yet every time I search it I only get fifteen results, sometimes the same 15, sometimes a random 15. it depends what time of day I search, I think. it’s very frustrating.

then, when I look under Manage and Comments, I only see the most recent 20 comments despite the fact that my dashboard reports that there are far more than that, and there’s no next/back page anywhere so I can see the rest of them. why is this?