There is no such thing as a contested sea zone.
Personally, I don’t think this should even occur. One round of sea combat only; if the defender survives the attacker must retreat (and can still do so even after a victory).
I can understand the logic behind a land force not being allowed to retreat after a victory - they have to consolidate their hold over the conquered tt.
But why would ships remain behind in an empty sea zone, especially if they can retreat back into a friendly port for repairs and/or reinforcements from newly launched ships? Unless they wish to launch amphibious assault or enact USW why should they be obliged to remain behind and quite possibly become sitting ducks for enemy fleets? A case of being punished for success?
The anomaly occurs when a player places new ships into a sea zone occupied by enemy fleet. Should a battle immediately occur? Or should the new ships only be “launched” in his next movement/combat cycle?