This will change in the next 1.17.1 update.
I've decided not to change it in 1.16.5 since it was a documented feature, and I don't want to break any existing builds (as unlikely as that might be).

Changed in 1.17.1-2.1.0a

This isn't actually a bug. It's a documented feature (https://github.com/dannydjdk/Tiny-Redstone/wiki/Tiny-Components#tiny-piston--tiny-sticky-piston). However, it's worth considering changing it now. It made more sense with the 2d circuits, but with 3d circuits, we introduced the concept of components attaching to other components and "popping" off of under different circumstances.

@dannydjdk oh it was documented!
And now that you say it, I remember it a little bit too.