They are keys that do start with `__distarray_` but that (normally[1]) the context is not tracking.

Typically there shouldn't be any such keys, if there are, the context isn't tracking something it should be, but we do still want to be able to clean them out.

[1] 'normally' means that one called this after calling `cleanup_keys()` which removes all the keys the context is tracking. If you called this before `cleanup_keys()`, you would get the keys the engine is tracking as well.