Hi, I'm glad to find that someone else has the same problem! My 14 month old daughter has done this for quite some time, but not during a tantrum. She bangs her head against things just whenever she feels like it! (and she thinks it's funny!). Maybe it's a girl thing as my son never did this when he was little, but I'm hoping that it's something that they'll grow out of.
Hope you feel better knowing you're not the only one!
Caz