I had the same problem with the ceiling zombie during my 2nd trip through the mine, while conducting a trader quest.
On my first trip through an instance of this POI, which I happened upon while wandering, a ceiling nurse-zombie alerted on me after I stood up from crouch to gather a shroom. Prior to that, while stealth and using my bow, I had bestowed the Emperor's Peace upon a sleeping half-zombie and a sleeping hardhat-zombie in the same chamber.
On the second trip, for Trader Jen, a ceiling Moe just stood there, catatonic, even though I had just gone loud with a pipe machinegun on his buddies. Wanting to see what would happen, I left him alone and cleared out the rest of the POI. Ceiling Moe still did nothing. I came back to his room, jumped up and down, dug up the bags of fertilizer, mined a few blocks of stone, wasted a pipe bomb in the hole I made, and the guy just stood there, deaf to the world. Okay. Fine. I ruined his career as an adventurer, by shooting him in the knee with an arrow, and only then did he wake up.
