Why does catching AggregateException cause CA2000 dispose warning?

Question

The code below causes a code analysis warning CA2000, claiming that I need to dispose of getRequest along all code paths before it goes out of scope. Tweaking the code slightly, for example removing the when from the catch, eliminates the warning.

try
{
    using (var getRequest = new HttpRequestMessage(HttpMethod.Get, uri))
    {
        using (var result = client.SendAsync(getRequest).Result)
        {
        }
    }
}
catch (AggregateException exc) when (exc.InnerExceptions.Count >= 0)
{
}

On which code path is dispose not called, and why does catch/when affect things?

Note: I'm using VS2015's built in code analysis. CA2000 is in the managed binary analysis ruleset, and is (for me) unchecked by default for new solutions. (VS2017 also emits the same warnings)