On Windows 8.1 vous pouvez get rid of it avec these paramètres:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Taskband]
"NumThumbnails"=dword:00000000
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"ExtendedUIHoverTime"=dword:41fffffe
Import them and redémarrer Explorer. See here.