To say the least I have had troubles similar to yours, and my solution was that the objects were indeed saved to their own groups BUT they were not exported, which for me caused them to show up in map maker but not in-game. I always make sure that whenever I play with Object Maker I save AND export the object to whatever group I put it in.
Try this and see what happens, not everyone who makes the objects exports them, and not every time is FH going to realize the object has been exported if downloaded from a source.