It sounds like the problem is in the RS232 loop.
I think the odds are against you, that switching the initial control type from IR to IP is going to have any change on this. Hopefully I'm wrong.

Are you using approved cables for the RS232 interconnects? Proper lengths between each TV? I'm thinking this could be a capacitance problem on the cable.
I don't have a lot of RS232 experience but I have always heard from experts that do, capacitance on an RS232 run can wreck havoc and cause weird things to happen.