In a Plone 5.1.5 site, (upgraded from Plone 5.0.6 once), I just noticed versioning is not working properly. Making a new Plone site on the same Zope gives same result.
Steps to reproduce:
Install a new site, add a Page, edit it, save: versioning works.
Add a new Dexterity Content type TTW (MyType), add rich text behavior and versioning behavior
Add 'MyType', edit it, save it
/@@historyview shows no edits (it only shows 'State change (publish etc')
I installed collective.revisionmanager and it only shows histories for 'Pages'
Looking in /portal_types I see both content types have
For reference: Versioning works in Plone 5.0.6 without any (extra) entry in port_diff tool (in other words: versioning worked before the site was upgraded to 5.1.5.
Update: I checked Plone 5.2 and it is the same (not working). If this is expected behavior: maybe we should change the description of 'versioning behavior to something like: Versioning support with CMFEditions. You also need to add your portal type to /portal_diff tool in the ZMI' ?