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I tried to google, but cannot find any result. It might be I did something wrong. I have a very simple straight forward basic upload module. Similar to the "demo upload" in vaadin demo page. However I noticed that if the file size is about 20KB, the uploadFinished event is called twice. I tried big files (700KB), they are always correct (only one get saved). but for small files, sometimes they got saved twice, sometimes once, because the save method is in the uploadFinished event.