We've been using the control for awhile now and wanted to upgrade to get drag and drop. Downloaded the latest DLL to test. Mostly, it's okay, but with IE10/11 there's a bug with the drag and drop.
If there is already a file present in the database for a particular field, the codebehind creates a link to download the file and a button to delete it. If there is no file, we create the uploader control to upload one.
It works fine in all situations except IE10/11 if we start the page with a file present.
Page is generated with the file download link/delete button.
Hit delete, postback is triggered, page is re-drawn with the uploader control.
In IE only at this point, draging a file to the <span> tag that's set as a dropzone doesn't trigger the onupload event. We get a progress bar, then we just get the queue panel with the filename in it.
In all other cases (other browsers, or IE if the uploader control was created first and not in a postback) it works fine.
Hitting the browser refresh button clears the queue panel and from that point, drag and drop works fine.
Using the button to select a file always works.
So it's just something IE specific IF the control was created during a postback. I'm at a loss what it could be.