Using Firefox (or Chromium), go to global index page, select actions menu Create new item, Upload files, use file selector to select 2 image files, open, click Start All button: file server shows traceback in attached file - MultiFileUpload.txt.
Meanwhile, Firefox has rather strange display of resulting index page. After closing upload popup and clicking the global index tab the resulting page shows the image files were uploaded OK and may be viewed.
-- snip opened
#327 as a separate issue: IE9 offers to download a file during upload.
Using Firefox or Chromium to upload one file at a time works OK.