How to prevent thumbnails

I have a bunch of avi files encoded with divx 6.7. I used 4cc changer to show them as xvid.
In the media center window they used to show up as a blue box with the title inside.
After I upgraded to divx 6.8, the system builds a thumbnail for each file, without the title. The title only shows up when the mouse hovers over the file.
The divx 6.8 version solved several annoyong bugs in 6.7, so I would like to keep it.

Is there any way to prevent media center from building the thumbnails?

Thanks
Joe