I do have to wonder why the system was designed to allow pitch trim with the AP engaged.
On every type I've flown, manual pitch trim with the AP engaged disconnects the autopilot immediately. Indeed on one, using the pitch trim to disengage the autopilot was the most common method used by pilots (the other was the MCP button) as the master cutout switch on the yoke also took out the YD, which was typically not taken out until minimums.