check it out with '
media player classic'(it's free) (link not the original OSS homepage, but a very good mod of the original, as the
original has been inactive for quite some time) right click the video screen, and select 'filters' and it will tell you what codecs/filters are actually being used at the time, that can help you track down what is up.
some of them have options (like divx) you can reach from there, maybe premier just disabled a built in interlace filter?(it's on by default with the divx codec, and maybe for others) or it might have just left a codec behind, or re-ordered your codec priorities.
gspot (it's free) will tell you what codecs the video was actually made with and thus what you would probably want to show up as the active filter in media player classic when you play it.
and
DSFMgr (and...it's free

) will show you all codecs on your system, and check their priority settings, sometimes codecs annoyingly force higher prioritization and mess up normal viewing (the last 2 divx builds have annoyingly over prioritized it so it's used in preference to xvid even if it's told not to decode generic MP4)