Effect level does not show for amplifiers greater than 5 (levels greater than 6)

Potion affects aren't showing the number after level 6 of the affect. I'm not too certain if this is a bug or not.

Steps to reproduce:

1. Run /effect @s regeneration 30 5
2. Open the Mob Effects HUD
3. Note whether or not the effect level appears
4. Run /effect @s regeneration 30 6
5. Note whether or not the effect level appears

Observed result:
The effect level for amplifiers greater than 5 (level 6) does not show at all.

Expected result:
The effect level for amplifiers greater than 5 (level 6) show at least until 9 (level 10).