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On the demo that you are looking at, cancel button is not shown since an ajax post-back occurs when
is fired. The remove and cancel buttons are shown only before the post-back on which uploaded file is tranferred from the temporary directory to the real destination directory where it should be uploaded. If you make this post-back not right away when the file is uploaded in the temp directory , but based on some other user action which make post-back the only possible solution is to hide this buttons with the following styles:
.ruButton .ruRemove, .RadUpload .ruRemove,
ruButton .ruCancel, .RadUpload .ruCancel
the Telerik team