OOPS sorry, I did send a reply, but it did not "stick".
The problem is understood and has to be dealt with in SmartPropoPlus.
I can reproduce the problem, so it's a matter of time. Can't promise how much though. I'll probably start with a private version that I'll write for you, but you will have to be patient with me and help me test it.
Let me explain what I think we have here:
SmartPropo & SmartPropoPlus assume a wave pattern with abrupt rises and drops. A slow rise like we see here confuses SmartPropoPlus: First it thinks it is a very long 7th channel, then it understand that it is a long low and it waits for a short high for the first channel. etc. I will have to think of a way to recognize such patterns.
I think the reason to this problem is the combination of a lack of a pull-up resistor in the Tx and an insufficient sink capabilities of the Mic input (After all, it was designed for a Microphone).
So, give me a few days to make some preliminary solution.
Shaul