Piston duplicates blocks on its branches when qc-ed.

[Yi Cao]

Client version: 1.12.2
Server OS: macOS
Cuberite Commit id: 3b2a501

Build a structure like this

A - Stick-able block (e.g. stone)
S - Slime block
R - Redstone block
P - Piston

 SA
 S
 S
RS
 P

And it will duplicate A.

However the duplicated blocks behave like ghost blocks since they drop nothing when mined.