there are no raw's, just scanned tifs...
I have a problem with Bridge, too. After Bridge generates high quality thumbnails and previews for my RAW and Tiff files (which range from 8Mb to 36Mb), if I then process one of the RAW files, or alter one of the Tiffs, I get the same generic thumbnail when I go back to Bridge. Bridge does not automatically generate the preview/thumbnail for the image, no matter how long I wait.
I have my ACR and Bridge preferences set to Generate High Quality Thumbnails, and to distribute sidecar files to the current folder whenever possible. One forum member suggested making a folder specifically for the purpose of dragging the generic thumbnails to it, waiting for the HQ thumbnails to be generated, and then dragging them back to your work folder.
I also find that after selecting one or more of the generic thumbnails, I can go to the Edit menu and click on Generate High Quality Thumbnails. However, sometimes that choice remains grayed out. Go figure.