Can’t change Freshness date format

I’m trying to set the Freshness date format to Custom, using the setting m-d-Y

(What I really want is mm-dd-YYYY, if the rest of the coding is required. The example for Y-m-d shows “2017-01-10” as the result, so I figured I could invert the code order and get what I’m looking for.)

The Custom field consistently reverts to F j, Y every time I attempt to apply my changes.

BBPress 2.5.12, WP 4.7, bbp Style Pack 3.4.0 running locally under MAMP 1.9.6 with PHP version 5.3.5. I’m using a child theme based on GeneratePress 1.2.41 with version 1.2.92 of the GeneratePress Premium plug-in.

Any suggestions?