Is this problem consistent or intermittent with your MBA? Mine usually sleeps normally while connected to external power but sometimes it'll still show up in Finder's sidebar on other systems after closing the cover.

If I put the MBA to sleep when it's unplugged, it immediately sleeps, it NEVER sleeps when plugged into the wall or when I close the lid. The only way I can get it to sleep is to sleep it on the battery, then when the power is connected, it will stay asleep. I have spoken with Apple, the said they were going to release a firmware update so am very disappointed that this update has not dealt with the problem.

Thanks for explaining how it's predictably reproducible on your MBA. Fortunately mine doesn't have that problem and the occasional mysteriously random lockups have stopped for a few months.