Possible Client 2 SP3 regression?

I'm using Client 2 SP3 and LDAP Contextless Login on Windows 7 x64 in a Citrix XenDesktop VDI trial. If I log in as myself or any user in my context it will go in fine. If a user in another context tries, they get the infamous "you are already logged into the network as user XXX, do you still want to log in as user YYY?" error, and it's always the same user (myself). This issue was supposedly resolved in Client 2 SP1 IR5

So far I've tried:

removing the context from the default login profile as suggested in a TID and on the forums
setting and unsetting the "save profile after initial login" option
setting and unsetting the TSAutoAdminLogin option in the registry

My next step is to rip out every instance of my user name from the registry to see if I can stop it from pulling my user name.

Has anyone else seen this issue, or is this a possible regression of the pre IR5 bug?

Any help is appreciated.