I have experienced this aswell. As mentioned in:
http://forums.adobe.com/message/4138626
and http://forums.adobe.com/thread/948417?tstart=0
My lightroom has after two weeks of playing with a fully working raw file corrupted it.
This is what the photo looked like originally http://500px.com/photo/14737987
As of today, I tried to reexport it with a diffrent watermark, the raw file corrupted. It exports a corrupted jpg and when I delete the .xmp metadatafile and try to import it again (same happens with it now when trying to import it to photoshop) the raw file now renders as corrupted in all software.
I have tried every possible way to reimport it, its just plain broken. If this should happen to my whole portfolio I would cry.