Thank you for the additional information about the current configuration and the screencast. After further testing we managed to reproduce the issue in IE 10 under localhost, when multiple files are sent simultaneously. Nevertheless the issue is not reproducible, when the application is hosted on full IIS and the site is not
opened through localhost, but through the server name over the network. If you would like to support the localhost scenario, I would suggest you to enable the batch option
of the async upload, which will force the files to be uploaded in a single request.
Please let me know if this information was helpful for you.
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