Okay, so the async modified is used to indicate that the asynchronous statement will be used.
There is a bit of overhead adding async to tests, so, we don't actually instantiate the code that handles Async unless the async attribute is in the Before, After or Test. If you don't place the async in these tags [Test(async)] and attempt to use the async code. Async.whatever... you will get an error.
Regarding the ui, attribute, the same concept was intended to apply for ui elements... in other words we wouldn't build the necessary infrastructure.. that is an optimization and right now is not in play. so you will not see different behavior with or without the ui.
If I copy your code directly from below and paste it in my environment it passes.
how are you running locally? i have replaced the FU swcs that are in the built-in plugin in eclipse with the 4.1 RC1 swcs. the async call always times outs.
i will try running from ant.
Running from both Flash Builder and Ant.