Double PistonExtender: Sand on top falling in between pistons

Following setup:
top repeater set to 1
bottom repeater set to 3
bottom piston is sticky
top piston is regular

if you hit the Lever 3 times (irrelevant of how much times passing in between activations) die Sand on top of the pistons will fall through the top piston and land between pistons, therefore rendering the mechanism useless