Remote Desktop Connection Manager throws an error when logging off a group

I'm using Microsoft's Remote Desktop Connection Manager on Windows 7 x64 Ultimate. I have several groups of servers, all under a single parent, sharing domain credentials.

Some of my groups can be logged off as a group, using the option "Log off group". But, one of my newer groups cannot be logged off as a group. I have some servers that cannot even be logged off individually from the "Log off server" option. I have to use the Logoff command from inside the guest.

Unable to log off from <group>
Reason: Unable to enumerate remote sessions

The "servers" that cannot be logged off individually or as a group using the RDC Manager menu options are Windows 7 machines. The "servers" that do logoff properly are Windows Server 2008 R2.

So, for now, it seems like Windows 7 is the issue.