mate-appearance-properties continues to run in background after closing, with one cpu core at 100% indefinitely

[d-d-2]

I am running Linux Mint 18.1 Serena, MATE edition, with all updates installed.

STR:

1. Open mate-appearance-properties
2. Close it
3. Run 'top' or 'htop' in terminal to observe cpu usage

Expected:

mate-appearance-properties should shut down its process when it is closed.

Actual:

One cpu core is at 100% with mate-appearance-properties still running over an hour after I closed the application.

Happens once/sometimes/always?:

I think it happens every time.

Extra notes:

when I run mate-mint-properties from the terminal, this is the output I get:

$ mate-appearance-properties

(mate-appearance-properties:10450): Gtk-WARNING **: Unknown property: GtkNotebook.expand

(mate-appearance-properties:10451): Gtk-WARNING **: Unable to locate theme engine in module_path: "oxygen-gtk",