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Cefiar
That said, the pull-ups/pull-downs are supposed to kick in when the tristate buffers are "disconnected" in Z mode, so I'm guessing that the tristate buffers are actually somehow loading their outputs when they're not powered.
I think the issue is that with VCC unpowered, the pull-ups don't do anything. So if we assume that the DMN2075U will be closed, then the gate of the IRLB8743PBF is in a questionable state, being connected to VCC with a 10k resistor. I think something is causing VCC voltage to be high enough to open the IRLBs.