Did a few more tests.
Your description indicates it is an older one before the redesign and has Local Control Sensing.
The redesigned modules do not have Local Control Sensing. Sold as CFL friendly.
Only the small On Off sensing.That has to be there for proper operation.
The jumper in the wiki should stop it from going back on but will not remove the sensing voltage.
In that photo near the top left. Just below the Blue Capacitor is the diode.
There is another modification on other sources. That removed a diode.
I went full bore and removed the jumper,diode, a capacitor and resistor in one of mine as a test.
After I studied my corrected schematic. Shows just the diode and jumper would be needed. The capacitor and resistor are disconnected when the diode was removed.
X10 did not change the part numbers on the appliance and lamp modules.
So the only way to try and determine older or newer is the Date Code.
Side note:
You indicated you are using TM751 Transceivers.
They are not polite so if two send an on line message at the same time. It is possibly step on each others message.
Also RF control only on hard wired Unit Code 1. For sending and the internal relay.
The RR501 is polite and will try and not step on an ongoing message.
Can be set to Unit Code 1 or 9. Has a power line receiver in it.
So you can also use a controller to turn on and off its internal relay.
Along with an RF command.