'Wall' Enemy Popped Out of Wall During BOSS FIGHT?

[Neco the Sergal]

Is this normal? I don't even see this enemy in the Ammonomicon - I've only ran into it twice, it's a Wall that pops out, turns into an enemy sorta like the concrete enemies in Super Mario 64. Only, one popped out during Level 1's Boss Fight - was rather unexpected, presuming the developers probably didn't intend for an enemy to do this - so I'm reporting this as a potential bug.

[machina]

Wall Mimics can randomly appear throughout the Gungeon hiding in walls, and will become active if the player shoots them or gets too close. They chase the player and shoots bullets at them, and do not drop anything upon death.

[Rubel]

We've reduced the chances that they can spawn in boss rooms after player feedback, but yes, they can still spawn in boss rooms!

[Cericat]

First time i got it it was in my first room right next to the entrance door. killed me.

[Rat Distributor]

i ran into one for the first time today but it dropped the heavy boots, so i guess they have a chance to drop stuff