Data entries set with the restriction feature are still overwritable by others.
User X sets a new item with this:
https://gamejolt.com/api/game/v1_1/data-store/set/?game_id=XXX&key=Test&restriction_username=USER_X&restriction_user_token=TOKEN_X&format=json&signature=XYZ (data is provided via POST)
This returns success and I can see the item in the data store, but others are still able to overwrite it:
https://gamejolt.com/api/game/v1_1/data-store/set/?game_id=XXX&key=Test&format=json&signature=XYZ (data is provided via POST)