Remote Control Makes Computer Inaccessible Locally

Have a new Vista Business machine. User logs in remotely (RDP) from another
machine... and eventually logs out. Comes back to his Vista machine and
stands in front of it and tries to use it directly (not via RDP). The
display, mouse, keyboard are non-responsive. Try pushing on the power button
- no change. Power button is still lit. Go back to another computer and can
still RDP into it. Obviously, Vista is alive but not paying attention to its
local input/display devices any more.
Must REBOOT the machine to gain control from the local keyboard, mouse, and
display.
Not acceptable.
Thanks for any clues...