Seramas have upright tails and short backs with vertical wings..it is hard to achieve this continually even with good breeding. Make sure that you cull the non-seramas (or sell them as "just bantam" teeny cute pets)
If you dont cull your birds, the genes go bad quickly...and you will end up with NON-Seramas. Plus if you keep breeding the best, and looking for type, you will have a bird that is worth something! People keep selling the junk and calling it a Serama, and as this continues the breed just gets lower and lower quality.