Falling sand can replace pistons, destroying them

A vertical piston supporting a sand block used in a pulse shortener (contraption shown in the screenshots) vanishes and is replaced by the sand it was supporting. This device rus on a clock and is therefore activated repeatedly without player intervention.

It happened twice in my suvival world when I wasn't looking. I only noticed the vanished piston when the contraption it is attached to stopped working. The images show a clearer version of the bug.

(Note that when it happened the piston was resting on a solid block and not in the air as shown here)