I could look up your system specs, but you would make life a lot easier by supplying those data with your post.
>using Pr CS5.0
Is there some specific reason you have not installed the bug fix and enhancement updates?
All Adobe updates start here and select product, read to see if you need to install updates in number order, or if the updates are cumulative for the individual product http://www.adobe.com/downloads/updates/
More information needed for someone to help... please click these links and provide the requested information
-Information FAQ http://forums.adobe.com/message/4200840
-Effective questions http://forums.adobe.com/thread/416679
-How to get help quickly http://forums.adobe.com/thread/419406
Exactly what are you editing, and does your project match your video?
Please NOTE that the PPro CS6 screen may look a bit different (I use CS5)
For CS5 and later, the easy way to insure that your video and your project match
See 2nd post for picture of NEW ITEM process http://forums.adobe.com/thread/872666
-and a FAQ on sequence setting http://forums.adobe.com/message/3804341
When your project sequence is correct, you will not see a red line over your timeline at first import, before you do anything to the video
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below... a screen shot works well to SHOW people what you are doing
Actually I am running CS5.3. I guess I would leave the question at, "Is there any simple reason why an MP4 file reviews better forward than backward?"
Yes, because the file is stored from start to finish on the disk. Playing backwards means more head movements on the disk to move from the end to the start and the cache does not help, like it does when moving forward..
What you're seeing is petty normal for this type of media. I'd not worry too much about it.