The base class ResourceLoader handles the loading of the modificationCheckInterval property. However, if the property is not present, or not of the correct type (long), it changes the default to zero.
This issue is amplified by the fact, that ExtendedProperties#getLong(name,default) does not cast Integers to Long (But it accepts a String property).
The type requirements should either be documented or the code should be improved to support casts from Integer to Long. Neglecting this actually disables cache refreshing and is hard to find for users.