Thanks again for the report, David. The developer has addressed this problem in MJ Registry Watcher version 1.2.6.6, just released.
http://www.wilderssecurity.com/showpost.php?p=1425133&postcount=622
I have since got the latest version and I have now run an MBAM scan, got the alert and was able to find the allow sub-key, clicking that option brings up another window, you check the item in the list to exclude (only one in this case) and finally confirm the exclusion. I guess the two step process is to avoid accidental exclusion.
Ran MBAM again and this time no alert, so the exclusion of that sub-key is working as it should.
