Hi,
In your example the upload does actually stop when clicking the button, but that is not because you called the deleteAllInputFiles(), it is because in your example the button does a full postback of the page...
In your example, try setting AutoPostBack="false" on the button, then you will see it clearly in for example Fiddler, that the upload continues. Even the OnClientFileUploaded event will be called after the button was clicked...
Try this example with a large file (so you can click the button before it finishes):
Regards
Caesar