Error parsing with IgnoreUnknownArguments to true and IEnumerable<int> option

[alvarodl]

Hi. I am having problems similar to described in #776 but working with version 2.9.1.

My scenario is this:

using CommandLine;

namespace QuickStart
{
    class Program
    {
        public class Options
        {
            [Option('i', "input", Required = true, HelpText = "The name of the videos to split. E.g. media split -i file1.mp4 file2.mp4")]
            public IEnumerable<string> Input { get; set; } = new List<string>();

            [Option('s', "seconds", Required = true, HelpText = "A space separated list of seconds to split the video. E.g. media split -s 5 10")]
            public IEnumerable<int> Seconds { get; set; } = new List<int>();
        }

        static void Main(string[] args)
        {
            new Parser(with => { with.IgnoreUnknownArguments = true; })
                .ParseArguments<Options>(args)
                .WithParsed<Options>(o =>
                {
                    Console.WriteLine("Quick Start Example!");
                })
                .WithNotParsed(errors =>
                {
                    foreach (var e in errors)
                    {
                        Console.WriteLine($"Error: {e}");
                    }
                });
        }
    }
}

Being IgnoreUnknownArguments = true when I pass more parameters (ex. --input c:\temp\test.mp4 --seconds 2 4 --test1 xxxx) it returns

Error: CommandLine.BadFormatConversionError
Error: CommandLine.MissingRequiredOptionError (in seconds option)

If I change the type of Seconds to IEnumerable<string> it works correctly (this is going to be my workaround at this moment) but seems like library continues going crazy trying to parse unknown arguments in this scenario.