Ah, that's an issue that the display driver has when the system switches to Secure Desktop during privilege elevation. The ATI drivers on my Tablet PC deal with this much better than the NVIDIA ones on my desktop do.
Until a driver update fixes this, there's a workaround you can use. Hit Winkey + R and enter gpedit.msc in the Run box. Now, in the Group Policy Editor window, expand Computer Configuration > Windows Settings > Security Settings > Local Policies, and select Security Options. Then, in the right-side pane, scroll down and double-click the "User Account Control: Switch to secure desktop..." item and set it to Disabled.
This, unfortunately, disables a good security feature, but it's the only workaround until we get updated drivers that fix the flickering issue.