>>as far as i know the FB2.5 RC seam to be the best choice for now, but

still some index corruption ...

I am also experiencing this problem at a few of our largest sites. The
larger sites tend to start off on FB1.5.5 and get moved over to FB2.1
later, but they report these problems consistently no matter what the
version.

I have not tried FB2.5, I didn't think it was meant to be used in a live
environment yet?