Merely wondered if others had noticed something similar, but upon receiving this wonderful treasure I began to notice it would heal monsters rather than me, unless of course I killed them and proceeded to walk into the spell mine. Is it just me? Poor luck? Or is this an unintended event?
Well, from the code: since it's a spell mine and doesn't have the permanent flag, it goes off on the first monster/player that walks on it. The heal however requires taxa="Player", so it shouldn't heal the monsters, only make the spell mine go away. Mind you maybe the heal effect cannot be taxa restricted, and so it needs a subspell for this...
I noticed that similar thing in the code, and the more I tested the more it appeared as the monsters were the only ones causing the heal to proc, as it would spawn the spell mine on their tile. Apparently more digging is in order.