Try this and see if it helps:

navigate to control panel and display properties icon
select 'appearance'
select 'advanced'
select 'icon'
change the size from 32 to 31 and then apply or OK your way out

There has been this issue since before vista was longhorn. No one has the cause chased down as of yet but it seems to be because of the size configuration!
Hope that helps!


Display Properties
Appearance
Advanced
Choose 'Icon'
Change the size to '31'