The Special:CentralNoticeLogs's 'bannercontent' log does not log changes to banner content if the banner content has been changed directly in the MediaWiki namespace instead of within the extension.

Example:
https://meta.wikimedia.org/w/index.php?title=MediaWiki%3ACentralnotice-template-stewnoms&action=historysubmit&type=revision&diff=16232947&oldid=16232856
does not appear in https://meta.wikimedia.org/wiki/Special:CentralNoticeLogs?log=bannercontent

This might even be a security issue considering it makes it possible to "hide" edits from the CN log by simply using a different way of editing.