Yes. I feel like you are describing Max when he was that age as well. Here is an old thread you may want to check out.
http://www.yorkietalk.com/forums/gen...ever-stop.html
You may just have to try different methods until you find one that works. Max is almost a year old and he doesn't really do it anymore to me but my husband still sticks his fingers in his mouth with reinforces the behavior. They definitely grow out of it but you will have to do some training.
