Bread size problem

[DinaFine]

I waited til the dough had doubled in size & was well above the top of the tins but once in the oven they seem to have fallen down so that the cooked bread is only the height the tin

Am I doing something wrong or is this something I should expect?

sounds to me like it was overproofed which means left to rise too long. If you poke it a little and it doesnt spring back at all and even deflates a little, you have to take it out of the pans, re knead and let it rise again.