But as far as I can tell, I cannot switch it to manual? They always auto-separate, triggering also the ET sep, and indeed we are dead.
At least for me manual separation works fine (you have to push the button while they're still burning of course, otherwise auto-sep is triggered). The Shuttle has no option to defer separation (the switch position is called MAN/AUTO because manual override is only available before AUTO triggers).
Also, 3EO automatically triggers contingency logic, which means an emergency ET-sep. You have relatively high aerodynamical forces during first stage - and you have a big and heavy ET to yank around with absolutely insufficient thrusters. Not a good combo.
Again, none of this helps you since you have no attitude control to speak of once you separate...
Oh, and you're out of trim. Badly...
The former -- update_tank is not called except when delta_lon is equal to 0.0 - so something is _badly_ amiss somewhere... that's like memory getting overwritten or something...
Yes, that's remniscent of the one I posted on the mailing list - a routine mysteriously running
before its class is even initialized, for which there's no available code path. Something is messed up inside Nasal.