So this is a new feature which popped up in the previous enhancement builds to Netscaler Gateway Enhancement Build 123.1100.e
It it also available in Netscaler VPX since it is the same build and everything.
The feature is ICA Proxy Session Migration which allow us to migrate sessions between users. For instance if a user has an active ICA connection from his computer and forgets to log out and then starts a new connection from his home laptop or iPad, Netscaler would then migrate the existing ICA session to that user.
This feature can be found under Netscaler Gateway vServer
So this only works if the vServer is set to basic mode, and will not function if the vServer is set in SmartAccess mode (even thou you do not get any error message if you do the switch.
You can of course do this switch in the CLI as well.
set vpn vserver x.x.x.x -icaProxySessionMigration ON
I can also mention that the 10.5 Netscaler beta is available from citrix to download http://bit.ly/1hTQxPV (This requires special access since this in a locked beta at the moment.