In the attached save,
the piston falsefully treat the life-1 piston part as one of its kind and extend in a wrong direction
(It should goes down but it goes left)
Since the bug will not appear if the particles are placed in different order,
this should be a bug related to order.

Twist: a seemingly minor bug usually get you hard when you do not bother to get rid of it.
It seems like that when piston is checking for direction of expansion, it counts those "extend arm"(PSTN with life 1) and in one case, it is happening with any particle order.
I have no idea if this is really how it is supposed to work or just mistake.
If you think this is a feature, fine and I will take it(a.k.a. abuse it)
Or just get rid of this troublesome bug that is disrupting complex piston structures