Disease does not appear on the left most side of the party buff bar like almost every other debuff in the game.

Frequency: 100%
Party or solo: Party
Area and coordinates: Anywhere where mobs use Disease (First/Last boss of Ampdapor Keep)
Steps:
1. Form a party
2. Allow a party member to get diseased (the first and last boss of Ampdapor Keep both inflict this status effect)
3. Look at the status effects to the right of their name in the party window. Normally debuffs (status effects with negative effects) get sorted to the left and are displayed before the positive buffs. With Disease, it gets sorted in with the buffs, often not even showing up in the party window. The problem is very easy to identify with a party member with a lot of self buffs, such as a Monk.
(optional)4. Allow a party member to be inflicted with any other status effect (Paralyze, Poison, Slow, Heavy, Bleed effects or DoTs)
(optional)5. This new status effect (that is not Disease) will always appear first in the buff list, allowing easy identification for healers to Esuna/Leeches it.

Why is this a bug? (since someone saw it fit to mark this as "not a bug")
Paralyze, Poison, Heavy, pretty much every other Esuna-able debuff in the game is sorted in a certain way. Disease and Inmunity Down however are flagged incorrectly, and are not sorted in this same manner. Consistency is important with these things, especially when a bug like this can hide a very important piece of information from a healer.