Std Link - missing sub element visibility in a linked Arch Building Part [edited]

[PMac]

Hi All, this has stumped me.

Trying to link an Arch Building Part into a target file.

Have created a box and a cylinder in an attached Source file. Have taken copies of both these objects and placed them in a Building Part.

Have created a Std Link in the attached target file. The linked BP Label and Level display OK but never the actual objects that are sub-elements within the BP. I expected to see a BP Label, Level, a red Box001 and a red Cylinder001.

Can someone please explain why I am unable to see the BP elements in the target 3D view, noting that they do show in the treeview? What have I missed?

I could Import the links, but doesn't that defeat the purpose of building small objects in an external file? I might as well have created all objects in one file.

[edit - forgot to include]
OS: Linux Mint 20 (X-Cinnamon/cinnamon)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: b5dc3887db550faa64b03377b901ef40dc07c970
Python version: 3.8.5
Qt version: 5.12.8
Coin version: 4.0.0
OCC version: 7.3.0
Locale: English/New Zealand (en_NZ)