@Fred_C, thanks for pointing this out.
I tested the Rhino 4 installers. Rhino 4 uses the .tb toolbar file format stored in
C:\ProgramData\McNeel\Rhinoceros\4.0
- Uninstalling Rhino 4 deletes the default.tb.
- Rhino 4 SR installers do not overwrite the default.tb.
The toolbar file format was changed to .rui in Rhino 5. The default.rui is stored in
C:\Users\<User Name>\AppData\Roaming\McNeel\Rhinoceros\5.0\UI
- Uninstalling Rhino 5 does not delete the default.rui. (This is the difference.)
- A new installation does not overwrite the default.rui.
- Rhino 5 SR installers do not overwrite the default.rui.
The fresh copy of the default.rui is stored in
C:\ProgramData\McNeel\Rhinoceros\5.0\Packages\ui (any).rhi
The .rhi is a zip file. The ToolbarReset command extracts the fresh default.rui to replace the existing default.rui.
The Importance of Saving Your Custom Work Environment [McNeel Wiki] is updated to reflect the fact. Thanks.