T520 Thin Client doesn't disconnect properly

I have HP T520 clients, running thinOS, connecting to XenDesktop BDI sessions using a web browser in Connection Manager. They log in through the NetScaler and launch the Citrix session successfully. They can work within that session, but if the session disconnects, either by the user selecting "disconnect" from within the session or from a timeout, the client simply displays the last thing displayed prior to the disconnect. They see the session graphics even though the session has disconnected. The only way to end the display nightmare and get back to the ThinOS desktop is to cycle the power.

Any ideas?