The 'unstable' releases we might get must be fairly stable ones for which they just want to seek out the last few bugs the internal testers might have overlooked
It's build 342 that I seemed to get a few problems on for the first time ever on any build of rf2
( not necessarily rf2's fault but things that only seem to effect rf2 as if it's became a tad more sensitive )
I don't know the nature of the problems you're experiencing, but the current build CTD'd on me a couple of times, which wasnt so with earlier ones. Difficult to appoint a culprit though.
In the recent past, Tim unstickied threads about new builds/content after about a month or so So I don't think it does mean anything, but then again, it also might