From USB Complete, 5th Ed:
A self-powered USB 2.0 device may draw up to 100 mA from the bus any time the device isn’t in the Suspend state. This capability enables the device’s USB interface to
function if a device’s power supply is off and the host detects and enumerates the device. Otherwise, if a device’s pull-up is bus powered and the rest of the interface is
self powered, the host will detect the device but won’t be able to communicate with it.