Jim, Half the battle of fixing a bug is reliably creating it and I'm striking out.
I'm not sure how far you want to go for a solution. Reinstalling may or may not help but live boot indicates it might.
Another option, short of reinstalling but not a trivial change, is install the Mate 1.14 PPA:
Again, this is a complete overhaul of Mate and takes a while to install. While this PPA is maintained by Ubuntu-Mate's Project Leader, it's also arguably unofficial. I run it, BTW. 