This Tweak will help you how to get rid of this problem
How To clear the Past Items or Icons list in the TaskBar, perform the following steps:
1.Open Regedit Navigate to:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\TrayNotify
2.Delete the IconStreams and PastIconsStream values
3.Open Task Manager, click the Processes tab, click Explorer.exe , and then click End Process .
4.In Task Manager, click File , click New Task , type explorer , and then click OK .