I also tried to reverse engineer the issue and had success.
In its initial, errant, state switching between "simple" and "expert" didn't do anything. So then I tried deleting all of the .BIN files in the main Content folder so it would essentially be a reset of my profile. With new .BIN files created when I ran TS again, the switch between "simple" and "expert" resolved the problem immediately. But yes, absolutely a DTG issue.
One other thing I found out is that it the same error also messed up the keyboard mappings for diesel locos and DMUs, not electrics though.
It's been an exhausting one. Tomorrow I will just drive trains! Thank you all, bonne nuit.