RDS CAL Usage Report

Hi,

We have 250 User Cals installed on our Windows 2008 R2 RDS Farm. If I run the CAL Uasge report it tells me that the "Installed CALs" is 250 and the "CALs in Use" is 46. If I then check RDS Manager I can see more than 70 active users are connected. Am I missing something here?  I thought "CALs in use" would tally with the amount of users connected. 

Thanks.