I have not had any of those issues, and you're the first person to report them among thousands of people. (excluding copy-paste here, which is just another feature request).
> if you try to import a map from a save file, say to edit a campaign map, the map will not save when playing it
Why would an editor map save when you are playing it, and how are you importing campaign maps/saves when there's no way to import or edit those without accessing internal game files? Are you expecting the editing of a map to affect the save it came from? Are you trying to hit 'save' after importing the (nameless) save and expecting it to work without specifying a map name? I just tried doing this and didn't run into a single issue.
> if you try to make a copy of a prebuilt map and add waves and an enemy spawn it won’t work
What does "won't work" mean? Does it crash? Does nothing happen? Does the map not save? Do the waves not appear? Do the spawnpoints not appear? Does it spawn the wrong waves? What are you trying to do?
> mirror mechanics
Menu>Generate>Mirror>Apply. Look around the menus before reporting a feature as missing or broken.