I don't work for Zimbra, I'm just here to help people. I'm trying to wean
my users from it, since they use the web client. The fact that you're using a web client introduces certain limitations, that's an inescapable fact.
However, if you want to see a feature (like having the option for both columns) included, you might want to search
Bugzilla to see if anyone else has suggested that, or file your own enhancement request.