Placing a button right above the ground will have mobs thinking them as "blocks" so they try to get up bu going on top of it but they actually can't.
MCPE-99901
Mobs think buttons are blocks
Resolved
Duplicate
0
duplicates MCPE-49772
this is already resolved in the beta versions, however there is a bug report intending to revert this specific change: MCPE-99698