ok seems not only rap on your stream so i'll tell
i _guess_ probably it assumes that video is 30fps, so bitrate that should be used is needed_br * 30 / your_fps
i maybe wrong as i never liked on2's plugin and used mine
some background info:
on2 made very crappy nsv plugin for their codec. seems they simply did find & replace on sdk example although added that useless config box in nsv plugin...
i discovered that their and mine plugins don't "signal" when encoded frame is keyframe so i asked on2 how to recognise keyframe...
silence... waited few weeks. nothing...
spend some time watching nsv streams in hexeditor
browsed a bit msdn fond how to set framerate info for vfw codec, wrote http://home.pages.at/slavas/txt/vp6x.txt
and "normal" plugin
as then was summer and etc only in september i told on2 to fix at least keyframe marking
they fixed and said "thank you"
but i _guess_ they don't set proper framerate as sdk sample missing it too