Assembly Browser doesn't dissemble async/await functions

A function like this:

public async Task MyFunction(CancellationToken cancellationToken) { }

is decompiled like this in the Assembly Browser:

[DebuggerHidden, AsyncStateMachine(typeof(MyClass.<MyFunction>c__async1))]
public Task MyFunction(CancellationToken cancellationToken) { }

which is not valid C#

Similarly, any statements in the method body are not decompiled coherently.

I'm using the mono compiler on OS X.