I agree with Ed, I find stopbath for RA-4 necessary to avoid random color shifts, HOWEVER I think that I actually have figured out why I have this need in my shop. I use a safelight for color. A heavily ambered (with filters) 7wt that is waaaaay down at the other side of the shop and behind & around a corner. Perfectly safe till I get within three feet of the blix. Sooo, I have to be sure it is stopped before I get to the blix.
Ed, could this be similar to your situation? I have never tried without having the safelight on, so maybe it (the odd shaped "smudges" of discolor) would happen in spite of the safelight.