Inconsistency between builds.

We've got a puzzling problem. We have a blurred shader (uses grabTexture) in our game, it looks fine on my box (Mac, dunno if that info is necessary, but being verbose in case it's helpful), when seen on our other developer boxes (PC) the blurred shader is flipped.

Now, we did a build thinking that perhaps I had strange stuff on my box that was overriding things and that it'd all be consistent on the browser builds, but the problem persists, looks fine on my box, looks flipped on the other dev boxes, despite the fact that we are all viewing the app in browser.

How is this possible, and what's going on?