Help diagnosing broken theme(s)

Sorry if the title is somewhat inaccurate, I'm largely unfamiliar with MATE jargon.

I'm certain that all I did after a recent clean install, besides changing the system fonts, was install a bunch of software from the Ubuntu repository, could it be something I installed that is causing certain windows to look like this:

and though I can't replicate in now after a reboot, the About Caja window was full-on GNOME sytle headerbar with the buttons up top.

Also sorry if I should be supplying further details about my system, please let me know what I should be specifying. Thanks!

(I'm on UM 16.04.2 on an X201 ThinkPad)

Your last image is due to an already reported bug.

Feel free to mark yourself as affected.