doesn't work
with the newest calibre I still can change the title to whatever I like, it shows as "Twilight". I didn't check in my kindle yet, but the kindle previewer does pretty much the same job.
I think it has something to do with the database name. Attached the same file, shown in previewer and the metadata in mobi2mobiGUI - in the "window in the window" you can see as first line Database Name: Twilight. BTW, the file is the updated metadata-file as saved in my calibre library - not the original imported file.