Verifying: I checked my Word 2016 installation. This is not a bug or anomaly, it is the way the program works. There are no options to change it. Re-installing will not help.

The command with the lines around it is the one that has the focus (the screen for that command is showing on the screen).

Here is a similar screenshot from Word 2010. There they use a box of a different color. In both versions, if you point at a different command with your mouse pointer but have not yet clicked on it, you get a little box. In the screenshot below, Info has the focus and is on my backstage screen; the mouse is pointed at the Open command.

00 deleteme 2.png

Again, not subject to user modification.

Like Stefan, I am curious as to why this is a problem for you.