I still don't quite get it - I see only three possibilities how users might pick up each other's settings:
-They share the same account on the same computer
-The settings are stored in a shared location, which uses Merged isolation mode (network drives, by default; also the spool directory...)
-The ThinApp package is configured to put the Sandbox in a shared location
*Maybe* if you use ThinApp for packaging, and then stream over Citrix, but why would you do that?