Highside Driver leaking when GND is unconnected
This is an Integrated Circuit, meaning that a lot of smart components are integrated within, including logic and ESD protective rings etc. etc. When dealing with integrated circuits, you don't arbitrary connect pins to live voltage, so simple rules of electricians do not apply. You connect the IC in accord with manufacturer's specifications, to your cables, and then apply power. Otherwise anything can happen, like unwanted triac-latch effect that shorts everything and smokes your circuit.

If you really need a "hot plug" capability, your connectors must be designed/selected to connect ground first, power next, and the rest after.