Adjustment brush tool on new macbook air i7

Hello all,

I have been looking all over the place trying to find an answer to an issue I am experiencing with Aperture 3.1.3. Just to let you guys know I have the most up to date version from the app store.

Problem: resizing the brush (ie: two finger up/down on the trackpad or sliding the slider for "Brush size") allows me to see the brush circle grow but when I get to a certain size, it suddently stops growing, the circle instead moves up (or down if i am resizing downwards). to understand this better, it stops resizing and looks like I am simply moving the circle slowly over my picture... If I keep sliding the "Brush size" up, the circle eventually comes back to its original position and continues at a much larger size until the end.

recap: brush size -- gets bigger when sliding -- stops -- circle moves up/down -- resets to original position on screen -- starts growing again but at much larger size until slider reaches end.

Just to note, I have an Imac as well with the most updated version of aperture and Lion installed and the application works fine on there.. but not on my brand new macbook air. other than that issue with the brush size, everything is smooth and fast like it is supposed to be..

My guess: perhaps it is a video card issue as the macbook air i7 is an intel 3000 and the imac is nvidia.. not sure though.

Attempt at fixing: I tried uninstalling, reinstalling (twice), tried repairing library, resetting pram just in case, and still no luck.. obviously.

Would be great if someone could help me with this one..

Thanks