Arcane Implement Mastery question

[Phoenix8008]

For the Arcane Implement Mastery in the Wizard class, for the Wand of Accuracy it says you can:
"Once per encounter as a free action, you gain a bonus to a single attack roll equal to your Dexterity modifier." when wielding your wand.

What happens if the power you are using is a burst that you have to roll multiple hit rolls against multiple targets? Do you get the bonus for all these rolls, or just one of them?

 

[Aage]

"Once per encounter as a free action, you gain a bonus to a single attack roll equal to your Dexterity modifier."

Emphasis mine

 

[shadowlance]

It'll be all of the rolls at my table...but I'm not sure what the official ruling will be on that one.

Heck, I'd even give the bonus to any secondary or tertiary attacks....basically all of the attack rolls for a single use of a single power.

From the quoted bit of text (assuming that's the actual text in the book), it sure sounds like you should only get it for one roll though.