OC.Notification.showTemporary() does not consider parameter timeout

When passing a “timeout” > 10 to the function, e. g.:
OC.Notification.showTemporary(status_text, {timeout:
this._notification_timeout_in_seconds, isHTML: true});

the temporary notifications are not consistently displayed for the specified duration. Is this intended behaviour, or maybe a bug, or am I doing something wrong?

Cheers, Jörg.