when the part turn on, capacictor across the winding and the output diode causes the first peak, and  reverse recovery of the output  diode result in the peak current too. So the problem can be improved with less capacitive charge to winding and output diode, but it is not easy.

regards

I understand the issues with the turn-on spike due to transformer capacitance, and reverse recovery.

My question is whether there is something related to the output shorted case whch makes it so much higher than the normal case.

At short circuit, the power supply always runs at CCM, and thus the initial current and the reverse recovery make the peak higher.

Regards