Old thread, but some technical info:
There is no protection or current limiting on any of the typical controllers I've ever worked on or examined schematics/etc of, against this kind of fault. (I'm sure there are controllers that do have some protection; I just haven't seen those)
The LVPS doesn't typically have any form of over- or under- voltage protection, or overcurrent, etc. Most of them use a simple LM317 to feed a 7805, with the simplest (cheapest) possible versions of the circuits to use them. There are more and more that use a form of SMPS instead, at least for the LM317 portion, but they may still use a 7805 for that part. Most probably use the low-power versions, allowing even less output current before damage.
I have a Grinfineon here that due to an internal wiring swap on the ebrake connector was repeatedly having it's 5v shorted to ground everytime I braked (which since braking stops the controller from driving the motor didnt' have any unexpected behavior to tell me something might be wrong, until it failed). Eventually the 5v system failed--it didn't just take out the 7805, either, as replacing that didnt' fix it. I did not get back to repairing it at the time because of other things that happened, since I had put a spare controller on, so I don't know the full extent of the damage. Someday I hope to get back to it...but no guarantees on that.
Some of them have a diode on the output of the 5v to the halls, which theoretically** would prevent phase voltage from feeding back into the 5v line in the event of motor cable damage leading to a short between a phase and the 5v line. This does not prevent the 5v line from shorting to ground, however, and doesn't limit the current much (only by reducing the voltage by the drop across the diode).
** in reality damage can still occur via the pullups in the signal lines, as there is a higher chance of a signal line short (more wires to happen to) than a 5v supply line short..and the only protection they have is the pullup resistor to 5v; this only limits current not voltage, and if current is very low the drop across the resistor may not be enough to prevent high voltage from damaging the 5v supply. In addition, the phase voltage may be passed directly into the MCU signal pins, and there is probably no protection against this...so the MCU can be destroyed this way, making any damage to the rest of the controller irrelevant, as MCU damage is unrepairable (unless you happen to have firmware to flash a new one with, which is unlikely).
