MemberAutoDataAttribute only auto generates values every second execution

Question

I tried to combine the member-data and auto data attribute this way:

using Xunit;
using Ploeh.AutoFixture.Xunit2;

class MemberAutoDataAttribute : CompositeDataAttribute
{
    public MemberAutoDataAttribute(string memberName)
        : base(
            new MemberDataAttribute(memberName),
            new AutoDataAttribute())
    {
    }
}

This is the test which implements it:

[Theory, MemberAutoData(nameof(CurrentWeatherResponses))]
public void ParseCurrentWeather_WeatherParsed(
    string response,
    Weather expectedWeather,
    TemperatureUnit tempUnit)
{
    // ...
}

And here is the CurrentWeatherResponses member:

public static IEnumerable<object[]> CurrentWeatherResponses
{
    get
    {
        yield return
            new object[]
            {
                CurrentWeatherResponse.ToString(),
                new Weather() {}
            };
    }
}

Why every second test execution all values are generated and not only the temperature unit?