I think it's alloy, might be other jokers does this as well. When you try to turn a basic card into a gold or steel one with death, the gold/steel card dies, regardless of being left or right. Position of cards doesn't matter. In my latest discovery, I noticed selling alloy fixed this in my current run, but I have seen this multiple times across runs.
It doesnt seem to happen early in the run, always later when you're in endless.