Thanks for the many quick responses!
I've updated RawTherapee to the latest version, and still encounter the same issue with JPGs developed from my raw images. However, if I develop them as TIF instead, they retain the same EXIF data but Paint.NET has no trouble opening them (https://www.dropbox.com/s/uqgaw82z47hh01b/DSC_2165.tif if needed for testing).
Is there somewhere I can download the previous release of Paint.NET to use until this issue is fixed?