Twenty eleven theme sub menu issue in ie7

I have an issue in sub menu of Twenty eleven theme,
STep to view the issue :
1. Add menu to navigation
2. ADD page in this format

• Home

• New page 1
• New page 2

• New page 2.2

Now: Hover on home and then on child menu and then last child menu. hold cursor for 2 sec.
Next : now again hover on home .You can see a backround color of last menu child.
This is css issue plz if any body know how to remove it do le me know .