Sticky pistons - unintended behaviour

I created a line of sticky pistons with normal pistons on top, to push sand up two blocks as part of a portcullis.  In this location, only the last piston pair is operating normally every time.  All the other pistons are not operating as expected.  I've cleared the area and rebuilt a number of times - same result.  I've built the kit in another location and had different results.  I was able to build one portcullis at another location that worked correctly.  Seems to be inconsistent.  See attached video.