did anyone try to press alt+strg+i ?
there you get information about the performance, for example fps.
if you talk about framedropping, afew dropped frames are not visible, even 12 frames per second would still look smooth, cartoons and flash movies are made at 12 fps.
if you notice really worse performance your framerate must be under 12 fps.
i only have this problem with mpg1 files. i have a slow computer and get normally with indeo or mjpg avis high frame rates.
i think the problem must be somewhere with the other installed software. for example sorenson squeeze installs a windows media runtime enviroment. after this i got some problems. or some codec packs are installing a lot of software wich have influence with the dealing with codecs.
maybe we should ask around , who is using wich software and windows, both the people with and the people without problems.