At the moment a keylisting may fail on the command line with an error but this error is not shown in Kleopatra.
Kleopatra does in that case the same as when no certificates are in the keyring and displays the welcome screen.
Instead an error message should be displayed.

The support case where this came up was a corrupt trustdb. In this case "gpg -k" on the cli returns "Error: The trustdb is corrupted." and helpful instructions how this can be fixed.