Vista Tutorial - Security Question

Anyone out there know about this?

<copied from a poster>

Even if it never happens, if there is two users logged in at the same
time, one is admin and has open a window, the other user can take
advantage of the open window that the admin uses and do everything an
admin would be able to do, as microsoft don't check from whom a command
comes, it just assumes that the user who uses the window is the one who
is logged into that session where it's displayed. There is a fix for
this, but requires a rewrite of explorer and make all GUI using
application to not work.