Image 1st bug: The piston can be powered through an air block. (It shouldn't work)
Image 2nd bug: The two pistons can only be powered once with this clock. (It should work)
Image 3rd bug a+b: The piston can be activated, when the block below the red wool was updated. (It shouldn't work)
Image 4th bug: Both pistons are powered by the redstone. (Only the upper piston should work)
Image 5th bug a+b: The piston turns on, when it's placed on the red wool. (It shouldn't work)
Image 6th bug: Only the lower two pistons work. (All pistons should work)