We have 3 fields we combine to 1 for a BOM.
Using the Coding $PRP"title1" $PRP"Title2" $PRP"Title3"
We use the custom property tab to enter our custom properties, this is not a part of that, this property is hidden inside the custom properties.. When you open a new part the linking exists as designed, when you click apply on the custom property tab the linking breaks, the coding may or may not be in the field we want, but the linking will not stick. I have a macro that we then need to run that deletes the property and re add's it with the same coding that is there and it works after that....
Also, it seems to be intermittent, because when I implemented this it worked, now about a month later it stopped working.