Bubble Columns do not form above height y=63

What I expected to happen was...:

Bubble columns created by placing water above Magma Blocks or Soul Sand
would behave similarly everywhere.

What actually happened was...:

Bubble Columns do not form above y=63.

Steps to Reproduce:
1. Place a water source directly above a Magma Block below y=63
2. Place a water source directly above a Magma Block above y=63
3. Observe that the same setup of blocks behaves differently