I don’t think you ever rotated the images in that case.
Windows is aware of metadata contained in the image that tells the device showing the image which way up the camera was when it was taken. It’s how your phone knows if an image is portrait or landscape.
For Xibo, you’ll need to load your images in to an editing application - such as Paint .net or GIMP - rotate them, and save. Now they are indeed actually rotated in the files they’ll be shown as you expect in Xibo when you upload them again.
This isn’t a bug, and we don’t plan to add photo editing features in to Xibo. There is plenty of freely available software to do that already out there.