Just upgraded from 2011, and kind of figured everything for the Toolbox wouldn't transfer cleanly. But I didn't expect this.
I use the linked material property within the Toolbox because when a new (unassigned config) fastener is added, the material is set to <not specified> by default regardless of whether you have that material set in the default config. My custom property list of linked materials was around 15, but only one would be enabled for any particular component. Upon initial inspection of those custom Toolbox components that were tied to a material, clicking on the material property displayed only the enabled material prior to the upgrade. However, not all were correct, but almost all.
I was happy about what I saw, thinking that the linked material custom property was on a per component basis. I then proceeded to correct the remaining components by removing the incorrect material(s) and replacing it with the correct one. I did this all in one go and saved the changes.
I then double-checked earlier components for correctness, and discovered their material had changed to the material of the last component I modified. Sure enough, every one of my custom components had been changed to this material. I looked at the Material custom property, and it confirmed my worst fear - the linked Material property had not been saved on a per component basis.
Resigned to recreating my original list of materials, I added all the missing materials only to discover that if the list size exceeds ten, it gets truncated to the max limit after you finish creating it and select another component to modify (or any folder). I then tested whether this limit applied to text-based custom properties, but it doesn't.
<Sigh> Oh, well. I've come to expect this crap from their programmers. If anyone has a workaround, I'd appreciate the help.