File Upload node (Valid File Extensions)

I was unable to find suitable answer on the forum, so my question is:

Using File Upload node on the server side (Web portal) and setting Valid File Extensions to ".txt,.csv" (as stated in Node description) does not set file filter on Open file dialog (it just shows All files).

Did I incorrectly write the setting value into the node?

Yes, unfortunately that is correct. We use Vaadin as our application server for the WebPortal and its file upload component does not support to filter file extensions in the file chooser dialog. There might be an option to do that in future releases, but for now this is an expected behaviour.