Why are you even editing read only files? what is it you hope to achieve by doing that? Editing a file that you dont want changed is well...
And this was a deliberate feature, introduced in 5.37 which you can see in
https://calibre-ebook.com/whats-new
And it was introduced precisely to prevent someone from losing hours of work if they happen to edit a file that was readonly for a random reason and they dont know how to fix file permissions (which is surprisingly common).
And yes there could be a warning dialog, but implementing one is too much effort for this, at least for me, patches welcome.