Ok, i know what's going wrong.
gnome-disk-utility is 3.0.2-3 and remmina is 1.0.0-4+deb7u1 are GTK3 applications and expected gtk3-4.x .
But current Menta is optimized for GTK3-8 because current GTK3 upstream version is 3.8 and some distros using 3.8.
Here we several probs.
-- your distro is too old and too conservative.
-- every little change in GTK3 breaks a theme and driving theme artist crazy.
-- every theme needs to be optimized for 4 GTK3 versions, (GTK3-2/-4/-6/-8)
This is imposible to do for mate-themes, because the result is to provide 4 several mate-themes packages.
Sorry, i suggest to downgrade to mate-themes-1.6.0, here Menta is opimized for GTK3-6 but it seems to work also with GTK3-4 as you said.
But i did a lot of other fixes and improvements for 1.6.1.
At my githup repo i've created 4 mate-themes-extra package for every GTK3 version.
see https://github.com/NiceandGently?tab=repositories viewtopic.php?f=16&t=250
Hope this will explain the issue and help you a bit.