Has improper value for
From LRDE
"Has improper value for" is a predefined property that tracks input errors for irregular value annotations and is provided by Semantic MediaWiki. In most cases it is caused by a type mismatch or a value restriction. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.
This is a property of type Page.