Oddly, with HP5+ I've gotten the purple tinge doing a clip-test of the fixer, but after the whole developing process on the same roll there is no tinge. However, when fixing the actual negatives, I was more vigorous in agitation, and fixed triple the clearing time (because of the tinge). I've searched APUG, and the best I could find was related to fixing, though am not positive. I don't worry too much at the moment as I'm still just testing and learning B&W, so I have no "important" photos yet.
I was using HC-110 at the time, and Kodak's powdered fixer.