My Janome 3160 QDC does that even when I am sewing very slow. I was told that oiling that little hole under the bobbin might solve the problem. I did and it helped but it still jumps up and binds every once in a while.
I have had the same problem with my Janome Q1260. Have brought mine back to the dealer twice. Second time he replaced the bobbin casing. He keeps telling me I am the problem, seems to think I am not using properly. I found that if I slowed the speed that I am sewing down, it doesn't jam up. It makes me laugh, because one of the marketing benefits they claim is how quickly you can sew with the Janome. While my machine was in the shop, I used my backup machine Singer 201, and it sewed like a dream!