I have seen that before :S Don't know exactly why it occures though..

This is what I could find with a little eye-to-eye contact with google.
http://adobe.groupbrowser.com/archive/t-39313.html
http://www.adobe.com/support/techdocs/330616.html

http://www.slashcam.de/info/adobe-premiere...leme-83503.html
Some german site oO

- http://38.119.81.13/messageview.cfm?catid=..._MSGDBTABLE=arc
:/ Maybe you should take a look on this one