If you use vigilance, while already detecting invisible through another means (potion/spell) and you use vigilance again when the 'detect invis' wears off, it allows you to, instead of saying the "You are already fully Vigilant" as usual. So it seems that vigilance is not covering 'detect invis' due to already being affected by it, then needing to be "reset" it. Seems there is a bug here somewhere.

You are affected by:
Commune: 'bless' modifies save vs spell by -14 for 33 hours.
Commune: 'bless' modifies hit roll by 7 for 33 hours.
Skill: 'vigilance' for 31 hours.
Skill: 'vigilance' for 31 hours.
Commune: 'armor' modifies armor class by -20 for 7 hours.
Spell: 'detect invis' for 1 hours.

Your eyes no longer pierce the shroud of invisibility.

vig
You increase your vigilance against unseen foes.

Yeah, not quite right.

When you call vigilance, and you already have a detect up, you only get the detects you don't have up. If you lose the detect, you can call vigilance again to get it back.