I have the same Rosewill R912E 19" LCD and encountered the exact same problem. I was able to resolve it by installing "nvidia-settings" driver config utility. In the driver utility I found that the setting under Flat Panel Scaling "Force Full GPU Scaling" was checked. As soon as I unchecked it, the bouncing box disappeared. Thought I'd share.
Let me clarify what I actually did to the /etc/X11/xorg.conf
VendorName "NVIDIA Corporation"
BoardName "GeForce 8600 GT"
Option "FlatPanelProperties" "DFP-0: Scaling = Native"