There seams to be a big fault in FZ properties.
In FZ part Edit you can add different properties, but they don't work in Inspector.
More weirdness.
I was able to delete the value of a part in properties/part number with FZ Edit, and it came through Inspector as blank, but when I entered a value in Inspector part number, the value now wouldn't delete in FZ Edit. I had to delete the whole part number section in FZ Edit, but when I reopened the part in FZ Edit part number was back, but blank.
I think if you can't make parts technically perfect with the graphical tools, FZ has a big problem. Basically if you need to actually code parts to get them to work that is one step too far.