It does the same thing for Read-only files...
(BTW, shift + right click, "Open As Read Only" doesn't work)
Changed attributes of a word file to Read-only.
Open the file
Title bar says [filename] - Read-Only - Saved
A few seconds later the window refreshes. The word "Saved" disappears. The read only notification belatedly pops up in the upper right side of the window.
Upon closing the window, user is prompted to save.
If "Save" is clicked, the Save As dialog opens (as it would be expected to do if the RO file was actually changed).
Anyway, as a workaround, the new procedure is, open a file, start working, after "Saved to this PC disappears", stop working, click Save. "Saved to this PC" reappears and remains. Use the file as usual (in this case, without changing it, inadvertently or otherwise). When done, close the file as usual and not be prompted to Save the unchanged file and not giving it a double take and not question ones short term memory. Downside is the date on the file changes. In this circumstance, it rarely matters to me as they are usually "notes" files.
I hope this is a bug and not clever (one-drive) marketing. This is basic functionality that goes back to when I still had hair and PS2 mice roamed the Earth.