Oooh, this is interesting.
Since I am on a mac, I often play RPG Maker games with a browser on a localhost with MAMP, so I knew that if you play from the browser you can see save games from other RPG Maker games. However they are usually greyed out and not usable.
I guess that the reason why in this case you can select them is that both this game and the previous one share the same ID (in the System 2 tab). I could create a new ID, but I fear that doing this could make all the saved games created so far unusable. Since it looks like this issue is not preventing you to enjoy the game, I will just leave it like that for now.