Duduli, i just saw ur post

I am not sure about your case. I never heard anyone got backgroud-checked in canada or Mexico. but I do know two of my friends who recently went back to china got checked and they still remain in china waiting for the result.
When I was in the Vancouver US consulate yesterday, i was asked to do a finger print check, I was asked to my both index fingers on a scanner, and VO recorded on his computer.I guess they use it to search for terrorist/criminal match in their database.

You were on B1, it looks bad to VO, if i were u, I choose not to take the risk until I have my GC. I know it's difficult, but that's the risk you shall think about.