Terminal Services RDP Screen display flicking in Mac RDP connection

Hi;

One of my user who connect to my Windows 2003 Terminal Service server via RDP on his iMac, recently; he found that the screen is flicking after connection, the hour glass will display either.  The problem occurs after I did Windows update recently.  My user installed a new version of RDP from App Store but does not help.  I have not faced such problem while using the RDP on a Windows 7.

Any idea?

thanks!