Reproduction of U4-9904

MediaController.cs

using System.IO;
using System.Linq;
using System.Net;
using System.Web.Http;
using Umbraco.Core.Models;
using Umbraco.Web.WebApi;

namespace U4_9904.Controllers
{
    public class MediaTestController : UmbracoApiController
    {
        [HttpGet]
        public bool CreateImage(int timesToRun = 1, bool? withworkaround = null)
        {
            for (int i = 0; i < timesToRun; i++)
            {
                GetAndSaveImage(withworkaround ?? false);
            }

            return true;
        }

        private void GetAndSaveImage(bool withworkaround)
        {
            // Get the image from umbraco
            IMedia firstFolderWeCanFind = Services.MediaService.GetChildren(-1)
                .FirstOrDefault(m => m.ContentType.Alias == "Folder");
            if (firstFolderWeCanFind == null)
            {
                // make sure we have a folder
                firstFolderWeCanFind = Services.MediaService.CreateMedia("beautiful images", -1, "Folder");
                Services.MediaService.Save(firstFolderWeCanFind);
            }

            // Get the image from the interwebz
            string photoUrl = "https://picsum.photos/200/300/?random";
            WebRequest req = WebRequest.Create(photoUrl);
            WebResponse response = req.GetResponse();

            using (Stream stream = response.GetResponseStream())
            using (MemoryStream ms = new MemoryStream())
            {
                int count = 0;
                do
                {
                    byte[] buf = new byte[1024];
                    count = stream.Read(buf, 0, 1024);
                    ms.Write(buf, 0, count);
                } while (stream.CanRead && count > 0);

                //  b = ms.ToArray();
                ms.Position = 0;

                // Determine the internal filename
                int startIndex = photoUrl.LastIndexOf("/", System.StringComparison.Ordinal) + 1;
                var lenght = (photoUrl.IndexOf("?", startIndex, System.StringComparison.Ordinal) >= 0)
                    ? photoUrl.IndexOf("?", startIndex, System.StringComparison.Ordinal) - startIndex
                    : photoUrl.Length - startIndex;

                var fileName = photoUrl.Substring(startIndex, lenght);
                if (fileName == "")
                {
                    fileName = "random-image.jpg";
                }
                // Get the image from umbraco
                IMedia image = Services.MediaService.GetChildren(firstFolderWeCanFind.Id)
                    .FirstOrDefault(m => m.ContentType.Alias == "Image");

                if (image == null)
                {
                    image = Services.MediaService.CreateMedia(fileName, firstFolderWeCanFind, "Image");
                }
                else if (withworkaround == true)
                {
                    // https://issues.umbraco.org/issue/U4-9904
                    // Set the umbracoFile value to null, so that when SetValue is called 
                    // the 'old' value will be null and Umbraco will not try to delete the file
                    image.Properties["umbracoFile"].Value = null;
                }

                image.SetValue("umbracoFile", fileName, ms);
                Services.MediaService.Save(image);
            }
        }
    }
}