I see the Datetime issue, but still can't confirm the Date issue. Even on the demosite. Suspecting there's something up with the browsers JS Date function when using a different locale. Doesn't seam to be timezone based, but maybe language based causing the format to output differently. I don't know to be honest, but will begin debugging further and see if I can figure out what's going on. The Datetime issue is present when the site and user are both set to UTC the dropdown continues to offset by local, which could be part of the problem.
forge.joomlapolis.com/issues/6415