Ah, okay... Some old saves might indeed stop working... :( In the version I'm developing right now, I'm trying to be more careful about that.
About deleting saves, we’ve taken notice of that as well. Unfortunately, only version 0.7 and above will allow you to delete them. Since we implemented a completely custom GUI in 0.6, that specific feature hadn't been added yet.
We’re sorry for the inconvenience in the meantime :\