I've asked around and none of my contacts has seen this before. One missing detail is the exact version of CS3 - is it 10.0.1?
What happens when you do the following editing routine? Do a File > Export targeting a folder that's already shown in Lightroom, choose 16 bit TIF, and in the Export Actions choose Open in Photoshop CS3. After editing in CS3, save, and then do a sync back in Lightroom.
A similar routine is to tick Add to this Catalog in the Export Dialog box. Again, what happens?