Lots of acers have suffered wind burn this year, it seems. There have been several posts here recently telling the same story. One of mine has suffered, too. Provided the plant is basically healthy, next year's leaves should be fine.

My Garnet ones are exactly the same. It was the wind in my case (and moving them in leaf, witch is asking for trouble). Basically the wind causes water to evaporate faster than the roots can supply the leaf, so it browns off and early autumns.

Wind is becoming a real issue for these plants - here in London, I'd say we have a lot more windy days than we've ever had, its rare for the air to be still now. Part of climate change I'm afraid, so if you have a more sheltered, less windy spot for it, you could move it there when the tree is dormant during late autumn/winter. Wouldn't work here, areas which used to be sheltered in the garden downstairs now get the wind because there seems to be so much of it...