This behavior is expected as it is explained in the description section of this on-line demo
To execute focused item press the Enter key or Space key.
Please note that in IE is not possible to open the file dialog with Enter key - browser limitation.
This is valid for all input with upload type so to RadAsyncUpload as well.
That is why in case of IE we recommend adding additional instruction that space will open the dialog.
Hope this will be helpful.
the Telerik team
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