Why does CopyTo throw ArgumentOutOfRangeException?

Question

Why does CopyTo cause an exception? The code below it works perfect and is what i thought copyto would do.

using (var mem = new MemoryStream())
{
    using (var memin = new MemoryStream(v.body))
    using (var comp = new BZip2InputStream(memin))
    {
        //comp.CopyTo(mem); //Non-negative number required (System.ArgumentOutOfRangeException)
        var buf = new Byte[1024 * 4];
        int len=0;
        while ((len = comp.Read(buf, 0, buf.Length)) > 0)
        {
            mem.Write(buf, 0, len);
        }

    }

Answer 1

Its a bug in BZip2InputStream.Read(byte[] buffer, int offset, int count) . It returns -1 rather then 0. I reported the bug

Also CopyTo checks via != 0 rather then >0 as the code in the question does.