would have thought there was some sort of overload redundancy protection..
Well, there is (overload protection... and plenty of it). I don't think overload(in it's true technical sense) was the problem here. Drop your personal computer into the bath with the power still on.. and see what happens
For starters, I'm sure a few fuses would blow, leaving you with no power to your computer (Just like the airplane.. .except it had Battery/Standby power as a backup).
When some of the devices looking after electric bus control and power generation are underwater, you're obviously going to have a few problems
So, far, as part of fault-finding and defect analysis, just about all the elec system control computers and at least one generator have been replaced.
Rgds.
NSEU