ADUM1411 with unpowered VDD1

Hello,

I'm using 12pcs. ADuM1411 in oder to drive isolated ADCs with a single SPI. In my design I connected MISO to V_OD of all ADuMs.

The Idea was to use a transistor to power up VDD1 only when needed (i.e. when CS goes low).

Looking at the truth table in the datasheet, V_OD should go High-Z when VDD1 is unpowered and the output pins V_OA, V_OB and V_OC should go high (assuming CTRL1 is unconnected).

But this is not the case. Even with VDD1 completely disconnected the ADuM is still passing signals from V_IA to V_OA and VDD1 is **sourcing** 2.4V!! Only when I tie VDD1 to GND1 I can see the specified behavior (but then I have 50mA(!) running from VDD1 to GND1).
Is there anything I'm missing here?

Thanks in advance!

Detlef