looking at the waveform there is an inductance somewhere to limit the di/dt (all the wiring back to the supply & caps?) also still a resonant component from the way the current looks to be turning over, (C caps on rails and wiring inductance) you really need a low impedance pcb with wide tracks, double sided to remove all these extra wiring L's and better C's close to the H bridge to remove their effect also, then shorting the load will cause very large currents...!