After using https://meta.wikimedia.org/wiki/Special:CreateMassMessageList, the log entry is:
MZMcBride (talk | contribs | block) changed the content model of the page MassMessage/Lists/Wikipedia Library from "wikitext" to "MassMessageListContent" (Create mass message delivery list)
This is confusing because this was a page creation.
There's nothing MM specific about it since MM is just wrapping around the API. The same happens if you use Special:ChangeContentModel:
21:17, 2 March 2016 Legoktm (talk | contribs | block) changed the content model of the page User:Legoktm/plain text from "wikitext" to "plain text" (plain text!) (revert)
Change 274492 had a related patch set uploaded (by Legoktm):
Improve change content model log entry for page creations
New proposed log text:
21:30, 2 March 2016 10.0.2.2 (talk | block) created the page Also doesn't exist using a non-default content model of "plain text" (asdfdsfd)
Note that there is no "revert" link because there really isn't anything to revert back to.
Change 274492 merged by jenkins-bot:
Improve change content model log entry for page creations