seeing that you mentioned the red frames in the timeline, it seems to me that is a pagefile or memory access issue, as editing with HDV required realtime managemetn of GOP structure. If memory pukes or teh pagefile managment shits itself, then youve got a problem.

By the looks of it, it seems Vegas isnt handling the memory properly as back in teh days of V4 and V5, the "flash" filter used to flake out and throw in random frames. Now i personally wouldnt mind an ectual filter or script which randomises frames within a set range, but the point is that from my experience, there are some things Vegas needs work on, such as memory access and pagefile writing.
There is no doubt that editing HDV natively is alot more convenient for teh user, however its not convenient for teh system In turn, there is a constant rewrite of this pagefile and edit data and with MPG, you got the IBP gop issue as well, not to mention additional resolution to contend with.

So where does that leave you?

Tryu defrag ur Pagefile drive (be it on C drive or wherever you have your pagefile allocated.
This usually alleviated the problem. Another solution is to shut down vegas and reopen the project. 98% of the time, the issue will be gone, BUT thats not to say it wont come back.

This issue is not file specific. its a random occurance which locks onto the way Vegas tells the machine how a clip needs to be managed and displayed.

Another solution is to render out to cineform and see what you get from that.

I use cineform as despite the fact I can edit MPG, I jsut do not see the beenfits of MPG editign when most of my work is being colour graded or affected in some way shape or form