I was testing interactions when I discovered a few weird things. The first, pushing sideways with a piston on a waystone pushes half of the waystone, leaving a functional, but ugly thing behind.

Before activating piston

After activating piston

Secondly, pushing a waystone from the top does something similar, leaving the half that you pushed but breaking it off in a similar way. The broken half is not functional and you end up with a waystone in your inventory. The waystone in the back had a block under it so it didn't get pushed.

hotbar before

hotbar after (assembling the second test in the foreground and activating the piston is the only thing that I did in between these two pictures)

Until #167 is done, waystones need to be made immovable by pistons (some mod is probably allowing all tile entities to be moved).

The likely culprit for being able to move the waystones was quark.
However, this issue persisted after I had turned off that part of the mod. I even tested it with furnaces as a control.
Setting in quark on: furnaces moved, waystones bugged out.
Setting in quark off: furnaces stayed put, waystones bugged out.