Strange rust

FYI
I attempted to remove a deep, dark rust stain from a metal file a week ago. Our rust remover did a great job but minutes after flushing it out w/ 101, the area began to turn purplish gray. Rust remover immediatly removed the gray but again, as soon as I flushed it, it came back. I then retreated with RR, left it in the carpet for a week and returned to flush it out today. Again, the gray re-appeared. At this point, my only hope was Cody. He suggested dilluting the RR to a 1 part RR/ 10 parts H2o, applying to stain, blotting off excess and not flushing. Worked great!!
I thought this was worth sharing as it seemed very rare.