The only time I've seen anything do this was in early versions of speedpatch. If you're running and older version of that, do update it (or remove it). 125Mhz is unstable, and doesn't allow transition fast enough to handle all cases (missed calls, etc) which is why Nokia avoided using it in the first place.

Personally, I run 0/500/900 with a large step threshold and have no issues with low battery or lack in usability.