Having set some file constraints like max file size or max file count per upload (Upload compoent), a file rejected event is fired for every file, which do not meed conditions.
documentsUpload.addFileRejectedListener(new DefaultUploadFileRejectedListener());
For example, if i set max file count to 5 and I try to upload 8 files, a file rejected event is fired 3 times. Potencially showing multiple redundant notifications.
Docs: