It is normal to have Properties in your Control/Component whose default values are inherited from some other Control/Component.
In such cases you will normally prevent the designer from storing the property’s value in code (using either DefaultValue attribute or the ShouldSerializeXXX pattern). However, if that property is Localizable and Localization is turned on, then the property’s value will be forced to be stored in the resource. This will break your property-inheritance logic.
In the above case the MyControlButtonFont inherits its value from the Font property, if its value is not set. And you use null to determine whether the value is set or not.
But when Localization is ON, the property gets SET and you lose the inheritance logic.
You can avoid this by specifying an AmbientValue attribute for your property, as follows:
This will use the AmbientValue as the value to persist when there is default-value in your property. This will prevent your property from getting SET unnecessarily.