frame mystery

[blbyspidla]

Hello, I found out something disturbing: I use Koepi 1.0 Beta XVID codec and VirtualDubMod (the latest).
When I want to encode 100 frames (for example I set a start to 400th frame of my source and an end to 500th frame) I get only 99 frames in the final file!
When I tried DivX codec everything was OK. Any ideas whats wrong? thanx

[decryptit]

Perhaps a bug Koepi is still beta stick to divx.Until a stable release is out.