You're not actually placing gremlins in other peoples towns that you don't have. When you collect from friends and exit their town, without collecting all the gremlins, then the gremlins do not show up on gremlin total.
Say you have 5 gremlins when you start collecting. Then you place 5 gremlins in the first town. While collecting in that first friends town you receive 2 gremlins from ghost or haunting. Then you leave before the goo/gremlins collect or the collection message appears. When you go into your next friends town your gremlin count will be 0 but you actually have the two gremlins you collected from your previous neighbor. It will say you have 2 gremlins to give and when you give those two gremlins your gremlin count will say negative 2.
I hope that makes sense.