I noted that current Sparky Mate still uses mate-core in version 1.8.0+jessie. It seems to me that the current version is 1.8.0+7 (that's the one in testing), which apt (probably for alphanumeric reasons) considers older than 1.8.0+jessie, so the package won't be updated.
Another aspect: package mate-desktop-environment is not installed. My system (started as 3.5) ran well without it but apt-get autoremove wants to purge pluma and pluma-common without m-d-e so it would be safer to include m-d-e.
Edit: This should have gone into "Suggestions". Maybe you can move it there.