In memory powerup is only able to register a single item.

[perkinslr]

The Empowered._inMemoryPowerups is a dictionary mapping interfaces to objects, rather than mapping to a list (or some other collection) of objects. This means only the last registered item is kept, any previous in-memory-powerup is silently discarded.

Ideally, a list of objects should be supported, but failing that, the old object should be powered down first, or an exception should be thrown.