observer's image manufacturing

observer's image manufacturing:

Expected to happen:
No image should be remain

Actually happened:
image random manufacturing

Steps to Reproduce:
1. Put these blocks 1 block high from the ground:
("O" = observer block, "S" = Slime block, "P" = Sticky piston, "⟶" = facing)
1 block high, 2 block high
P⟶ S|||||||🡑 O
S ⟵P|||||||O 🡓
2. Active one of the piston
3. Block's image will manufacturing while machine working

Information(about the copy block):
1. Using /testforblock result "Block is air", but "observer" in F3 mode
2. Available to stand on it
3. place block and liquid will replace it
4. doesn't count to the piston max push count, if 12 blocks is infront of it, and with piston push, it will disappear
5. if every block piston push is copy block, the closest one to piston will disappear
6.boat with no one will get through it, but will stay on it when some one is on the boat, but minecart will always get through, no matter any one is on it