B737-300
Confusion; Troubleshooting; Workload; Distraction
Aircraft Equipment Problem Less Severe
Flight Crew FLC Overrode Automation; Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action
Aircraft
Aircraft X had a Rockwell MCP; the one with the small pushbuttons; instead of the traditional classic paddle switch MCP. It worked without incident our first leg.  During taxi out for the second leg; the First Officer (FO) asked; 'Do you want that?' and pointed to the CWS A light illuminated on the MCP. Somehow either it had engaged itself or we had somehow inadvertently pushed it. He looked puzzled. Since I was familiar to this from my Safety work and having had it previously; I said; I would explain this in-flight and pushed the autopilot disconnect button. We got the Autopilot Disconnect horn; and the CWS A light extinguished. We rechecked everything and took off. Everything worked fine the next two legs. I was fortunate to have a very sharp FO who first noticed the trim wheel moving without pilot input during taxi. It seems these new style MCPs may be incompatible with the older model aircraft. I know we have had several rejected takeoffs when the trim started to run with un-commanded pitch and roll commands during takeoff roll.It seems in the interest of safety we need to get a full understanding of this anomaly and either correct the situation or provide adequate training and or procedures to prevent this from creating an undesired aircraft state. NOTE: we didn't write it up because we couldn't tell if we had inadvertently pushed it or it had turned itself on. From a human factors perspective; it would be very easy to unknowingly lightly push it while the FO performs his flows.
Captain's leg. On taxiway C; CWS engaged on taxi out to departure runway in commanded engagement. I noticed that the trim wheel started to move as we were taxiing. I looked over to see if the Captain was trimming the aircraft and he wasn't. I looked up at the Mode Control Panel and saw the CWS light illuminated. I informed the Captain and he disconnected CWS using the autopilot disconnect switch. We discussed the issue prior to takeoff and he said some of the MCP panels have had a history of this. We briefed our departure to include watching to make sure it didn't happen again. It didn't nor did it happen from the [previous] leg. No other issues.
During taxi for takeoff; a B737 Mode Control Panel (MCP) Control Wheel Steering (CWS) engaged and began trimming the horizontal stabilizer. The First Officer caught the trim movement and disengaged CWS.