"Has improper value for" is a predefined property to track input errors for irregular value annotations that was likely caused by type or allowed value restrictions.
Example sentences from FOC V22 : [1] Fruits capsular, woody, dehiscence loculicidal and septicidal, [rarely irregular or fruits drupaceous ]. [2] inner tepals pale reddish maroon-brown, elliptic, of irregular lengths, 8–15 mm, emarginate-apiculate; +