I don't actually know if it's a bug or not,
but it's not very practical and hard to understand why editing,  in particular,  needs us to click on the "ok" and "apply" buttons instead of just pressing enter

Because in a message edit dialog box, it's ambiguous as to whether or not the user meant to insert a newline or to send the message. Actually, most people tend to think that in a dedicated editing window, enter will create a newline. You are right that it would probably be a good idea to have a shortcut to apply the edit and close the dialog box, though.