Even if you are flying directly above the location (creative) the piston will be placed pushing to the side, not upward.
Actually there seems to be a small sweetspot in which placing upward still works but it shrunk significantly compared to <=m14w05b.
Environment
jdk7u51,linux x64
Duplicate of MC-47459 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.