Delete 2003 commandbar from 2013 ribbon on closing workbook

Hello. I have the following code behind "ThisWorkbook" in a workbook originally written in Excel 1997 - 2003, but now being used in Excel 2013

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The intention is (obviously) to load a commandbar tied to the workbook when it is opened, end then (important) to unload it when the workbook closes.

When I do it in Excel 2013, I find that it does not unload the commandbar on exiting the workbook.
Worse still, when I open a different workbook based on the same template, the command bar attempts to launch macros in the earlier (closed) workbook.

I need a solution that will still enable the workbook to be opened in Excel 2003 as well as 2017 (I run it in compatibility mode and save with .xls extension).

Any help gratefully received.