Hi Joel
Thinking about it I'm really not sure how this would manifest itself if you are using the PTT jack on the front panel of HL2 to initiate TX. I have a footpedal connected to that jack for manual control of TX.
If I am using datamodes then of course the TX command is issued via CAT from the program in question. So to answer your question, I've tried to replicate your issue and I cannot. Disabling the TX DSP panel has no effect on whether I can initiate TX or not, either via HL2 PTT jack or via CAT from WSJT-X for example. Both work fine, including after band changes and start/stops of the radio.
Can I please ask, if you do not have the TX DSP panel open, then how are you initiating TX if not from either the PTT jack or the controlling program? Is there any chance that you are perhaps trying to use the keyboard space bar? With SDRC this only replicates the last use of the TX button so then you would see the behaviour that you are seeing. I understand this is standard Windows behaviour in many programs, that using the space bar repeats the last button pressed by the mouse, and this is exactly what you would see here. Unlike (I think?) Thetis, the keyboard space bar is not specifically meant to be used as shortcut to TX PTT in SDRC. It's just following standard Windows behaviour. I personally avoid this use of it.
73
Max