It you referring the to the check box Scale the fit the media. Photoshop will indeed do the necessary calculation and set in the value for the paper size you set in the printer settings.
No, I mean the one that says "scale" right before the fit media. When I click in that box to try and engter a vaule, it just goes wild increasing the value until I cancel. Ihave rebooted both PS and my computer but the problem persists. I have been using PS for years and have never experienced this problem.
When Photoshop starts doing strange things the fitst thing to try is resetting your Photoshop Preferences.