Both sides are right. I have lost a male rat when he was introduced back into the males cage, after literally hundreds of introductions and growing up with the same males. We believe it was an accident since there were no real heavy marks on him, but still the same.... he died.
He had just come out of the breeding tub, and in the morning he was dead. I felt terrible, and now I never let the males out of ear shot, and they are closely monitored all day after being reintroduced.
If the reaction is not normal, the males are all bathed and kept by themselves for a few days, then reintroduced into a new cleaned tub.