with the upcoming UP5 (within days i believe) will be possible to update to mate1.4 adding mate's repo
http://mate-desktop.org/install/#debian in due time packages.linuxmint will update as well from 1.2 to 1.4 but this is the quickest way, is also with some issues down the road
(only if you are following the default latest repos) because this mate repo "expects" testing and some library mismatches will happen after the end of the deep-freeze (but we're talking here about beginning next year)