Thanks again, Charles.
The results:

1. I can presume you are correct in saying "the problem is likely a poorly written Add-In". My employer has a Word add-in, which may very well be poorly written.
2. I've used the Add-In and found a completely different function for shortcut "Alt+Ctrl+M".
3. Due to organizational policies, I will just have to do without the comment adding shortcut functionality, until these policies change or the Add-in is fixed.

In my opinion, my question has been answered and this thread can be marked as solved.

A thousand thanks!