Check and see if any pots are push/pull
Nope, no push/pull pots. Good suggestion, though.
I do think cheechi was correct about the wiring, so we know it's working as intended. I will have to dig though to see if I could integrate a push/pull pot to act as a serial/parallel switch. I've never gotten into how those pots are built, but I have at least a passing understanding of electrical circuits and components...
Sorry to share the GAS!