[3 809 128 863] Challenge "Kill unique monsters in cruel", one completed while being in merciless

Hi,

While being in merciless, after killing a unique boss, I got the message :
"Kill unique monsters on cruel: Marcelus, the defaced (complete)"

I'm in Talisman, and I'm pretty sure I didn't kill this boss in cruel, probably skipped it.

Here is a screenshot taken at 20:43 CEST :


Not really a problem for playing, just reporting :)