By some reason drag and drop upload of .msi files fails silently.

After finding out that the same files uploads quite nicely by manually uploading through the plus-buttons and selecting it the old fashion way, we now have a workaround for the customer, so they can create their content on their pages as they wish.

We thought we had done something wrong with our configuration, web.config, mime-types, rewrites, request filtering etc. etc., a very time consuming investigation — but appearantly it's the drag and drop upload feature that fails.

Is this a real bug (that can be fixed) or a thing that can not be fixed due to browsers and API limitations?