I often work in StudioOne work that is not meant for CD release, and the mastering module is not quite happy with that.
For instance, right now I'm finishing off a project, a choir concert I recorded and my audio files are going to be set to a video of the event. Haven't lined up on the timeline all the songs yet, but I get a warning that I've exceeded the 80 minute limit that CD's are limited by.
A while back I was working on an audiobook that was to be released as a MP3CD and as as a MP3 download. In order to save space I wanted to deliver this as a mono file, but there's no way to do that in this mastering module. I was actually advised by someone at PreSonus to import my stereo master into the "song" part of StudioOne and set the master output as Mono, and thereby convert my master to mono. Pretty daft, since by doing that I lost all the metadata. I ended up finishing up that project in Wavelab, but I don't want to do that - I prefer the workflow in StudioOne.
There ought to be a setting where you can set what kind of project you're working on, if it's a Red Book compatioble CD, a digital release in some form or audio optimized for video or whatever. And it's just daft not to be able to deliver you work in one mono file.