Jerky (Div3?) play (skip -> keyframe)

[kbelles]

While playing a Div3, MPEG III, 720x368, 25fps file (on a 600Mhz P3, 384MB RAM, GeForce 256, SBLive!) BSPlay seems to get about 2/3 of the way playing between keyframes, then jerks forward to the keyframe and starts again.
This behaviour doesn't show up in either VirtualDub (which selects the DivX ;-) MPEG-4 Low-Motion codec) or the DivX Player 2.0 Alpha 5, with the same avi under the same load conditions. This seems to occur fairly often with the older encoded files. I have BSPlay set to use the Div4 encoder, and to load DivX ;-) settings, CPU and postprocessing set all the way up, film effect (what IS that, anyway?) off.
I'd rather use BSPlay given a choice, and I would hate to not be able to recommend it.

Any suggestions or help, or is this a bug?
-Kev