Hello there! I am new to the forum and am basically posting just to report this bug, but here we go:
(Sorry for forgetting some of the item names!)
I was playing as Redshift. On second floor I found the item that disables shields until next floor, but grants one shield point. Then I leveled up the minemaster (minesquisher?) perk.
On floor three, I picked up missile man (infinite rockets until hit) . As soon as I stepped on one of the mines, my shields were disabled and the missile man perk was gone.
Just to double check, I stepped on more identical mines and they did no damage to me.
I think that is pretty much it. I also used the time machine item to regenerate floor 3 once.
EDIT: upon further investigation, it seems like minemaster simply does not block damage for shields at all, at least for Green Envy.