Well, this apparently can happen when walking with Glommer during the night:
I was just walking and checking out everything (I just bought the game 3 days ago) when this happened. Apparenltly, when you move away from Glommer when he's sleeping he duplicates on the map
Walk with Glommer during the night, I was using the miner's hat, i don't know if that's important . When Glommer falls asllep move away from him a fair bit and wait until he comes to you. Then check the map, there should be multiple Glommer icons.