The bug

Placement of a double tall grass / double fern in the same block where it was already placed will cause the disappearance of the upper part of the grass.

How to reproduce

1. Place the double tall grass on the grass block
2. Try to place the same grass on the block where a double tall grass is already placed (in the lower part of the grass)

→ The upper part of the tall grass disappeared without particles nor sounds. If you are in Survival mode, the grass you tried to place will remain in inventory