In my world (any world that is on my ipad), when I place a piston, stand in front of it, and trigger it with a button, leaver, or pressure plate (including a red-stone path or direct action from the trigger to the piston), the piston will push me forward. This means I can create traps and people pushers etc...and fun games too! This also works when i attach a block to a sticky piston.

However, if someone joins my world, they do not get pushed forward by the piston, they just get nudged to one side.

I have tried this the other way round, I joined someone else's world and in their world, they were pushed by the piston and i was knocked sideways.

This issue also appears when you create a piston/slime-block lift...in my world, if i stand on a slime-block that is on top of a sticky piston, and then fire the piston, I will be pushed high into the air. When someone joins my world, they are just nudged off the piston/slime-block.

As before, i tested this with me joined to someone else's world and the same result.

Basically, the owner of a world is effected correctly by a piston or piston-block combination, and a joiner of a world is effected incorrectly.

We were joined on LAN, using two ipad Airs, both fully up to date on software.

To reproduce this, you will need two ipad airs and a world on each one. Then connect both ipads to the same LAN. One person should then open their world and the other person should join that world. Then you can create a people pusher or a piston/slime-block lift (or both) and each take turns trying to use the devices - you should see that the world owner is pushed/bounced but the world-joiner is only nudged sideways. you'll be able then to confirm the issue by repeating it but with the person who was the joiner becoming the world-owner on their ipad and the other person joining them on the same LAN.

Hope this is helpful as I was really looking forward to creating some tricky games etc with pistons for my mates to play, but I can't if the pistons work differently depending on whether the player is the world-owner or a LAN world-joiner