OK - I just repro'd, this time with NEF instead of CR2... still breaks the same.
I'm uploading you some files that will take about 30 minutes from now to get up on my FTP server. Links at bottom of this post. Here's what I did:
1. Created parent "PM_XMP_TESt" folder.
2. Created two folders, RAW and RAW2 in that folder.
3. Placed 7 NEF files in RAW.
4. In Bridge, set color temp of all 7 up to about 8K -- something very obvious since the "as shot" values were in 5K ballpark. Some other minor adjustments for un.
5. Set color class of first 5 images to 1 ("winner").
6. Of those 5 winners, tagged three of them.
7. Moved the tagged files into the RAW2 folder using PM.
8. Selected the 3 tagged files and group untagged them.
9. Moved them back into RAW using PM.
10. Went back into Bridge. The 3 moved files have had their XMP associations broken and appear unedited, despite presence of XMP file.
This is the state of the files that I'm uploading at the moment.
However, I tested a little further... In short, I determined that tagging a photo in place is all that is required to break XMP on my system. I did not even have to move the file to the other folder. Even though I initially perceived that as a requirement to break, it's not... Just tagging. I don't even have to untag: If I tag a file in the RAW folder, then go to Bridge, the file is immediately broken.
Here's my links:
http://davidhillphoto.com/previews/PM_XMP_TESt-working.ziphttp://davidhillphoto.com/previews/PM_XMP_TESt-broken.zipFirst upload is 70 percent complete now... Give it another 20 mins to finish.
p.s. -- Moving the file alone is not sufficient to break. I have moved the files several times without breaking. Additionally, I have re-confirmed my prior experience that using the EXIF time correction tool will also break the association. That file is not uploaded, but using my files all i had to to was shift the time on a file by one second to break the XMP.