I highly doubt i'm the first to encounter these bugs, just the first to report them. If you import a save from the saves folder in appdata and save it in editor, then go to custom game and play said map it wont save when you quit This happens for all maps imported in this way. And no, ofc i'm not expecting editing a save to change the file itself.
I tried making a copy of glacier, then adding in an enemy spawn, editing enemy waves checking all the boxes you need in the menu, but when you run it, you'll get wave timers and the audio cue when a wave starts, but no enemies spawn.
As for the mirror mechanics, i'm not talking about that stupid ore generation feature, i'm talking about a mirror than will mirror any tiles you place on one side of the map on the other side of the map, but I think you already knew I was talking about this.
Does that clarify things for you?