Diffusion ability buff removed when casting non-Blue Magic spells

Platform: Windows
ISP: Time Warner Cable
Type of Internet Connection: DSL
Internet Connection Speed: 15 Mbps
Date & Time: Jan. 1, 2016 12:35 PM PST, Jan. 2, 2016 3:22 PM PST, Jan. 4, 2016 10:51 AM PST, Jan. 5, 2016 8:02 AM PST
Frequency: Always
Character Name: Dillus
Race: TarutaruM
World: Sylph
Main Job: Blue Mage, Lv. 99
Support Job: Ninja, Lv. 49
Area and Coordinates: Reisenjima, ?-? (Flux 9)
Party or Solo: Party of myself and 5 trust NPCs
NPC Name: Amchuchu, August, Arciela II, Yoran-Oran, Qultada
Monster Name: None
Steps:
1. Activated Diffusion and Unbridled Learning in order to cast Mighty Guard on the party
2. Reapplied shadows using Utsusemi: Ni, before casting Mighty Guard, and Diffusion buff disappeared
3. Tested later by releasing Arciela II, using Diffusion, and summoning again
4. Arciela II was summoned and the Diffusion ability buff was removed from my character
5. Have tested multiple times since, using different spells, such as Protect, Shell, and Klimaform
6. All have yielded the same results