The problem is that the TS override was being reset when I pressed the Left or Right arrows on the Channel or VFO screen, and I didn't expect this to happen, and there was no indication that this was happening.
I also found both the TS override and the TG override are being cleared when I changed Zone, which I'm not sure is ideal functionality...
Looking deeper into the TS override system, it also was not functioning how it used to function
Because all my local repeaters are DMR MARC, they have fixed TS's per TG. I initially programmed the firmware to change TS if the TG has a TS override.
If I want override the TS on a TG that specifically has its own override, I'm happy to press Star after changing to that TG.
For TG's with no TS override, I expect the radio to stay on the same TS when I change to that TG (using Left or Right arrows)
When I've not overriden the TS manually or the TG does not have a TS override, I presume that the TS specified by the "Repeater Slot" parameter in the Channel data would be used.
Hence I think the priority of TS overrides order should be
1. Operator presses Star to override / change whatever TS the radio is currently set to. (Highest priority)
2. If a TG has a TS override
3. The "Repeater slot" / TS specified for the Channel
Changing the Channel should not change the TS or the TG (Unless a different TG list is used for the Channel)
Changing the Zone should not change the TS or the TG (Unless a different TG list is used for the Channel in the Zone)
As things stands I'm sure that its a bug that the TS is cleared every time the TG is changed, so I will be restoring the functionality to match the priority list as described above.
But, if anyone can see any reasons why this priority organisation would be a problem or not fit their use case, I'm happy to discuss how we could accommodate different use cases, possibly by an option which controls TS override priorities.