What is USB redirection multi user isolation?

When multi user isolation uses Microsoft or Citrix XenAPP connecting to cloud desk, more than one user connect to virtualization desk and redirection device at same time ,will see other user redirection devices (for example smart card ,flesh disk ).This will lead to information leak or security problems. Multi user isolation will solve this problem. It only allows user to redirection own device and wont be access to other user devices.