public class Counter
{
    public int Count;
}

public static class ExtBug
{
    public static void Empty(this Counter val)
    {}

    public static Counter Action(this Counter val)
    {
        val.Count++;
        return val;
    }

    public static void Test(Counter val)
    {
        val.Action().Empty();
    }
}

Inlining and removing of the Empty() method deletes the content of the Test() method, even though there is clearly an action being performed on the object.