So for roughly about a year there's been a glitch when you group items and then link that as the object to emit from an emitter. When you play the level and close it. The grouped objects are duplicated next to the emitter. This never used to be the case. I haven't used badlands because of this issue. Cos I love to create physic based particle effects. It never used to do this as of a year ago and I've waited nearly year hoping it'd change.
I've been aware of this glitch as I used an emitter to spawn a pretty complex contraption I made. I simply deleted the duplicated object every time I came back to work on that level. It's kind of annoying though, especially when your level is big and you emit a lot of contraptions.