Diffusion currently affects any and every spell cast on one's self, except it does not apply the buff to party members. It simply removes the buff and provides zero benefit whatsoever. Witnessed this multiple times with Utsusemi, Protect/Shell, and even with Trust magic. The Diffusion buff is removed and the next Blue Magic spell that you planned to Diffusion to the group is now only single-target. Extremely irritating for casting Mighty Guard or any powerful Unbridled Learning buff.