Suppose a device is transitioning from state A to state B. During state A, it can read certain private keys from the hidden fuses that are only accessible in state A but not in state B. The device reads the keys, performs operations using those keys, then transitions to state B, where those private keys should no longer be accessible.
(bad code)
During the transition from A to B, the device does not scrub the memory.
After the transition to state B, even though the private keys are no longer accessible directly from the fuses in state B, they can be accessed indirectly by reading the memory that contains the private keys.