Hi,
I'm not a urologist (or a medical professional) but from years of hanging around bladder cancer survivors and listening to their stories, I would say, no it's not so common for someone to react like this. There must be a reason. Someone mentioned they had bleeding post TUR that had to be cauterised.
Has it been determined what is the cause, has the doctor looked in there? I can only assume that since he had 2 BCG's post TUR, the bleeding is not from the TUR, but from the BCG treatments. I know that sometimes people react very badly to BCG and can't continue, and I've met a few who have had extensive bladder damage which necessitated cystectomy, but they had had more than 2 treatments...so...it's weird, I'm sorry.
About your other worry, the TUR was the act that removed the cancer. BCG is an insurance that there was nothing left and no seeding occurs, as well as a way to prevent any recurrence. So perhaps your son is already cancer free. A lot would depend on the stage and grade of the cancer, how aggressive it was. For example, many doctors recommended a second TUR for a T1, high grade (3) diagnosis, before doing BCG. If there is residual tumor found it would call for aggressive treatment and follow up.
This isn't done for Ta or lower grade tumors.
Wendy