Really, the system should have never let you put him on revokable waivers. I don't know if you "can't" do that in real life or not, but no one ever would, because in order to put someone who has been DFA'd in the minors, he has to clear irrevokable waivers - so the only thing putting him on revokable waivers might do would be to restrict who you can trade him to. Had he cleared revokable waivers and you had been then able to assign him somewhere, you really would have wound up exploiting a loophole.