we use the default search widget with multiple sources. When the source "All" is selected, and we type a search input string that doesn't exist, then a warning message "No results" appears and stays there.
If we select a specific source and not the option "All", then the warning message stays for some milliseconds and then disappears.
It is reproducible here:
Please let us know if it is a bug and if it is going to be included in any future release!