...probably the RF to PLC conversion is causing the lockup.
It has been many years since I played with X10 RF but...
There are minimal differences between standard and security RF signals. These differences are noted at... https://www.laser.com/dhouston/rf.html
Most X10 RF devices send 5 or more copies of the code. X10 RF-to-PLC transceivers start transmitting PLC as soon as they have decoded a valid RF code and ignore any further incoming RF while transmitting PLC.
Nice to hear from you Dave and thanks for taking the time to comment.
Yes the additional code transmitted by the security motion sensor is quite visible. The standard motion sensor is definitely more versatile though. There's nothing other than sensitivity that be adjusted on the security motion sensor so having the ability to adjust for night/day and on/off time is certainly a benefit.
I set the standard motion sensor to toggle via software so I can record momentary trips and I can override the minimum On state of one minute.
I've no real need for the House Code/Unit Code feature on the standard motion sensor so I'm wondering if I can disable this feature physically or if I can strip out this code between broadcast and receive.
Interestingly on a security console you can trick the console into revealing it's set of five RF codes for each of the allowable remotes you can enrol on the system.