Since downloading the latest version of the plugin, the timestamp/datestamp problem isn't as prevalent when changing to a custom status, but we're still having it happen.
I've been testing it over and over. It never seems to be a problem the first or second time (sometimes third) a post is saved with a custom status. But if it's moved to a second custom status or edited several times in another it puts in a timestamp and "Publish immediately" disappears.
I'm at a loss for figuring out what the problem is. It seems to be almost random. It's never the same amount of saves before it's caused, although it does seem to happen more often if it's moved from one custom status to another (it doesn't happen on the first save after the change, it's usually the second).
We have several statuses we use in the process (ready for editor and ready for staff are the most common), and it moves through at least one, if not two custom statuses along the way, so the problem is happening more often than I'd like.