Are you using a solid color background? If so try a picture and reboot (know bug)

If not try this registry fix:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System

Then add the following value as a DWORD (32 bit) [if existing just edit it]

DelayedDesktopSwitchTimeout

change value to 5 and reboot

Hope this helps!