Frequency:
Always

Class/Level:
Monk, lv 60

Party or Solo:
Both

When doing any rotation on Monk, using Snap Punch or Demolish will apply greased lightning the very moment the skill is activated. Every buff effect including form changes and self-buffs (such as twin snakes) is granted after a delay when the animation and damage are applied, except for greased lightning.
To better illustrate I've included a gif http://i.imgur.com/6jHiP5s.gifv
As you can see, form changes and twin snakes are applied midway or better through the gcd (depending on the animations, dragon kick and demolish are more exaggerated), but greased lightning is applied immediately.

It seems minor but having greased lightning apply on gcd start makes us lose about 2 seconds of the buff, forcing much stricter rotations and causing us to lose greased lightning stacks in fights we could previously retain them (such as t9 single meteor streams).

It has been bugged this way since Heavensward early access release, when prior to 3.0 greased lightning grant would be at the same time Coeurl form changes to Opo-opo form.