I had this problem last year - had 2 flowers in a 12 inch pot! not brilliant. Spoke to the manager in a local garden shop and he said the most likely thing is mice!!, they are so lightweight they can balance on the stems and chew out the buds, just leaving the very papery casing. Gave it a go again for this year and they weren't very successful either. Have now decided not to put any in pots again, but will be trying the trick of planting them in the ground about 15" deep (have heard that can be successful) they can then naturalise if they want to. I've not had any problems with daffodils in pots they were an absolute picture this year.