When you are in the System Tree, select "Actions" and then "Choose Columns" from the drop-up menu.
You probably chose "Agent Version" from the "Detected Systems" area, while I chose "Product Version (Agent)" from the "System" area. I have no issues with the Agent version being shown, with 20,000 managed machines and the same version as you are using.
Give it a shot!
Looks like I was using the Detected Systems property instead the Agent Property!
Thanks for your help!