I just noticed I still get this bug, or a variation of it. December 1st is the last day on the November month grid. I brew on Nov 11th and have the primary set for 21 days. The bar for primary runs through the last day, Dec 1st. When I click over to December to see where it ends I see that primary runs through to Dec 2nd. When I set the primary for 20 days it ends on Nov 30.
I have gotten the latest updates, including one I pulled down this morning.
I can provide screen shots if you need them.
Mike