Reverse current from motor driver causes buck converter to shut down
Dumping energy back into the power supply is generally a bad idea. You really should be using a diode to prevent that and deal with the motors energy some other way. 

If the 10A drop across the diode is more than you are willing to accept you should implement an "ideal" diode circuit that has a much lower on resistance and voltage drop. Here is a typical circuit.



Or there are devices available that do the same kind of function.

Here is a cross-post that talks about dealing with flyback energy.