I have an addin that uses ChangeCustomPropertyNotify and DeleteCustomPropertyNotify event handlers to track changes in model's custom properties. A few days ago I noticed that this tracking functionality sometimes not working. After some investigation I found out that this is happening if file is created by SW2018 and the custom properties list in the file properties dialog have an extra column "Linked":
This column completely unchecked and disabled. The model is not linked to anything. It is an isolated file, part or assembly. But in this case the SolidWorks just does not call my handlers when properties changed or deleted.
Why is this happening and how can I track custom property changing in SW2018?