In Cubase Pro 8.5.x, I’v noticed that when doing a mixdown to MP3 format, the metadata in the MP3 tag dialogue retains the information that was last input, in other words, the scope is global rather than local (project-specific). Is there any way of making this local, or is this something that fell through the cracks?
+1 For me, it makes sense to store it with the project arrangement file.
Sorry, I don’t understand. There doesn’t seem to be any way of specifying ID3 tag data apart from using the dialogue in Audio Mixdown.
It fell through the cracks. So no, it works as you have noticed.
If you want, search the feature request forum and support one of the requests to change this behavior.
Regards 
Yes, might do that. Just wanted to make sure I wasn’t missing anything in the user guide.