Piston activatation bug

I have a small mechanism to place rail on soulsand and then removes them both. I had one that had been created before 1.4 and it still works well even in 1.4.5.

I tried to make a new one in 1.4.5 but it does not work like the one that had been created before 1.4. This one makes the piston on the left get activated a second time, breaking the rails.

here is a video showing the bug: https://www.youtube.com/watch?v=5SwOVF2mKnk (sorry, but my recording software is broken)

EDIT: i have just tested this in the 4 possible orientations, the only one that does not seem to work is EAST: http://i.imgur.com/riA80.png

EDIT 2: i tried all 4 directions again, and now west didnt work