attack definition
Shard and Kobold, it all comes down to how you interpret attack in the spell. If a full attack full round action is a direct attack (and not the individual attacks that make them up) then the spell ends immediately after the multiple attacks of the full attack action. However, I think it is more reasonable to say a single attack is a direct attack whether it is a standard attack action or the first attack of a full attack action.
Do you allow your PCs to direct their attacks from a full attack action sequentially or do you require them to announce them all up front and follow through regardless of the results of the attacks? (If they are shooting arrows at goblins can they shoot as many as it takes to drop an individual and then move on to the next one or must they tacticaly guess at the beginning of their full attacks) If the events of a full attack all happened simultaneously then there could be no reacting to the effects of earlier attacks in the full round action.
Here is the srd quote on the full attack:
Full attack [Full][AoO: No]
Description: If a combatant gets more than one attack per action, the combatant must use the full attack action to use those additional attacks. A combatant does not need to specify the targets of a the attacks ahead of time. A combatant can see how the earlier attacks turn out before assigning the later ones.
The combatant may take a 5 ft. step before, after, or between the attacks.
If a combatant gets multiple attacks based on a combatant's base attack bonus, the combatant must make the attacks in order from highest bonus to lowest.
Deciding between an Attack or a Full Attack Action: After a combatant's first attack, if the combatant has not yet taken a 5-foot step, a combatant can decide to move instead of making a combatant's remaining attacks.
From this quote I would say that even the attacks of a full attack happen sequentially and invisibility can be ended between those attacks.