Might be sending the cached data? not a solution but have you tried deleting unmanged detector and creating a new one again?
P.S: For ex; When you run the scan from SEP 11.0.6:
It will find all the machines that DON'T have version 11.0.6 installed. So, if they have 11.05 or les or nothing they wil show up.
The same thing with 12.1:
12.1 will discover all cleints on the network running a version less than 12.1. So it will find all 11.0.6 clients as well.