LIghtroom 4 problem
I have never encountered anything like that. It sounds like a bug in LR.
It might be worth posting on the adobe LR forum:
I think that there is a list of known bugs in LR somewhere on the Adobe site.
Canon EOS 7D
Panasonic Lumix DMC-GF1
Panasonic Lumix DMC-GH2
Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS
Canon EF 50mm f/1.8 II