Windows 7 has introduced Jump List, which is basically a list of recent documents and unique features and links for that particular program, pinned favorites, etc. By default, Windows 7 displays 10 items in the Jump List, which can ofcourse always be changed via the Control Panel.
Jump List missing or disappeared permanently
If you find that suddenly your Jump List has gone missing or disappeared in Windows 7, you may want to try some of these troubleshooting steps:
1) First clear taskbar icons Jump List history in Windows 7 and see if it helps.
2) Else disable Taskbar Jump Lists in Windows 7 and re-enable them and now check if it has solved your problem.
3) If you find that your taskbar explorer icon Jump List not working in Windows 7, you should try to rebuild Jump Lists.
4) If none of this helps you, it is quite possible that the number of items in the Jump List has exceeded 999.
On a Windows 7 or a Windows Server 2008 R2 computer, the Jump List of an application could disappear permanently when you use the application to open or save a new item. This issue occurs when there are already 999 items in the Jump List.
To resolve this issue, what you can do is download and apply the update package mentioned in KB2607576. This should help resolve your issue.
Hope something here helps you solve your problem!