I prepared Cure Wounds by clicking on the spell in a 2nd level slot and it disabled Cure Wounds in the 1st level slot.
Casters should simply prepare spells without regard to slots. Cure Wounds, if prepared, should be available from 1st level slots and any higher slot.
A more straightforward UI would just have a list of know spells from which the player indicates which are prepared. Slots are irrelevant for preparation.
The same UI should also indicate spells that are always prepared (i.e. due to subclass) separately so the player understands why those don't need to be prepared.
The existing UI is confusing even for someone who knows 5e.
