Welcome to the forum.
Unfortunately, some are reporting the same thing. There are several similar threads, and most are very current on this forum.
I cannot directly help, as I am not doing the same from CS4. However, just today, I did the same Export at 400K and it was perfect - the difference was that I used PrPro 2.0!
Wish I had an answer for you, other than to say that others have the same, or very similar problems with CS4 and their threads might give you some resolution. I just do not recall an answer.
The Pixel Aspect Ratio in earlier version of Premiere wasn't technically correct. Now it is. I wonder if this might account for your observations. If so, there's nothing for it but to export at 328 x 240.
Thank you very much for this answers.
What do you think - should I'll write smoething like official question to Adobe help about this issue? The can help me more thank you?
Casue if it's true about incorrect aspekt ratio in previous versions 2.0 and 3.0 - their answer will be the same as you.