This is a bit crazy but I have this exact, well seems to be exact, problem only I am on Windows 2012 not 2008R2!!
support.microsoft.com/kb/2620656
what's most interesting is that you have to be on same LAN! So if I have a client connect into RDS environment from two PCs and two different users, each will see each others printers. If I get another client to do same they will also see each others printers but the two clients wont see each others. Seems like you need to have physical access to those printers to be able to see them from another session.
I looked in the registry and the HKCU\Software\Microsoft\Windows NT\CurrentVersion\Devices is populated with printers from other sessions and other sites even though its in HKCU as in current user, key word being "current".