Github user andruhon commented on the issue:
https://github.com/apache/wicket/pull/255
@svenmeier I've tried a better approach without modifying the js function
interface, it's just using multipart form data when possible, so works in IE9
as it used to work before.
See it in the branch:
https://github.com/andruhon/wicket/tree/try-multipart
Also updated the demo to use this snapshot:
https://github.com/andruhon/WicketDragAndDropFileAjaxUpload/tree/try-multipart
tested in Chrome, FF, IE 11 and in emulated IE9-10
If it looks like decent approach I can update my PR.
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