.NET: await event with timeout

Question

I'm attempting to create an async method which returns data from an event, or times out (and returns null). The code below loosely follows suggestions from other threads.

public async Task<Data> GetNextData(TimeSpan timeout)
        {
            var tcs = new TaskCompletionSource<Data>();

            //setup event handler
            var onEvent = new EventHandler<Data>((sender, args) =>
            {
                tcs.SetResult(args);
            });

            OnDataReceived += onEvent;

            //await result from handler or timeout
            Data result = null;

            if (await AwaitWithTimeout(tcs.Task, timeout))
            {
                result = tcs.Task.Result;
            }

            //cleanup
            OnDataReceived -= onEvent;

            return result;
        }

        private static async Task<bool> AwaitWithTimeout(Task task, TimeSpan timeout)
        {
            return await Task.WhenAny(Task.Delay(timeout), Task.Delay(timeout)) == task;
        }

The problem appears to be in AwaitWithTimeout, which should complete when either the task or the timeout complete. Instead, it never stops waiting. What I found strange is that, even when I replaced the contents of this method with something like await Task.Delay(timeout), it would never finish.

The following shows how I call it from the outer scope:

var foo = channel.GetNextData(TimeSpan.FromSeconds(5));
SendDataRequest();
foo.Wait();

Why does this code never complete?