A mangrove grown at a negative height creates leaves above it at 0 height

Summary:
Sometimes (very often) when growing a mangrove tree at negative height, leaves appear at zero height. You can use a flat world to easily reproduce the problem.

Steps to reproduce:

1. Place the mangrove propagule at a negative height.
2. Grow a tree out of it using bonemeal.
3. Look at the leaves that formed at 0 height.
4. If the leaves do not appear, repeat everything again.

Observed results:
When growing a mangrove tree at negative height, leaves appear at zero height.

Expected results:
Leaves should not appear above the tree.

Image: