Big thank you for the support. Version 25 upgrade seems pretty slick.
Since upgrading from 24, removing flash drives through the eject button in Mate is failing, saying not authorized, failure to eject. It doesn't seem to be a base system permissions problem, because the permissions for the device at /media/ mount point look fine, and it is possible to open a terminal and run umount /media/daXXX without having to su / sudo and this does unmount the drive. So the problem seems to be with the file manager?