I'm having a similiar issue in Firefox. If I edited in HTML editor in Classic, text was reverting to lowercase. Ok, I'll use Advanced if I want to paste HTML. Just now I needed to remove a period from client's content. Used Classic but didn't bother switching to HTML view because it was just a period. Sentence shifted to lowercase....as did the two cards beside it, just from removing a period in Classic (Inline) editor. Advanced is fine for me since I tend to write everything in an editor and copy paste so DNN doesn't log me out or hiccup (in 7) and tell me I'm editing/not editing/which is it/your content is gone! But clients are intimidated by "Advanced" sometimes, and you know, it shouldn't take three minutes to remove a period.
Also, at this rate, we won't have any browsers we're allowed to edit in by 2025. We already tell clients to avoid IE, now we should tell them to avoid Firefox and Safari? Can you see why dude used Wordpress for his kid's soccer team?