You may see various small amounts of rebate fog with your Rollei from time to time. I think it is just difficult to do everything right all the time;
Keep the load and rewind in the dark, keep the paper tight when doing both, etc. It's a kind of primitive system, if you think about it. Just work on your technique.
I have a 3.5T that occasionally has fogging up into the first frame or two, and I never know why.