Has anyone tried this ESXi patch to see if it fixes the problem?
PR774818: Black frames might appear around text boxes in an application running on Virtual Machine Hardware Version 8 or later. You might also observe this issue if any of the open application windows are moved across on the desktop. This issue occurs on virtual machines with Windows 7 guest operating system and View 5.0 PCoIP.
VMware ESXi 5.1, Patch ESXi510-201307401-BG: Updates esx-base and misc-drivers (2052144)
VMware ESXi 5.1, Patch Release ESXi510-201307001 (2052143)