Noticed this while playing Artifact Anarchy earlier. Triggering Massive Chop's secondary effect doesn't cause it to be revealed, leading to some potentially confusing situations.
This also happens with other cards that change rolls, such as harnesses if the armor they boost negates all the damage before it gets to the harness itself. I agree with Xayrn@, it would probably be more convenient considering that there's only a few cards that change rolls like that so there's no real purpose to hiding them after they're used.
Known bug. Talked to Jon about it. Seems there's no super easy fix, and we're not going to delay EttSC for it. We should fix it eventually.
Another possible bug with Massive Chop involved: It occured while playing Artifact Anarchy. Two of my characters (A and B) had blocks in hand while one character (A) had also a Massive Chop. An enemy chopped both (not a Massive Chop). As far as I remember (not 100% sure), the dice roll for both blocks (A and B) was substracted by 2 instead of only for character A. It might be worth looking into it.