Problem with expand child of active items with BOOK Menu

Hi ..

I have this menu block (builded by the BOOK ROOT ):

ROOT
- A
-A1
-A2
-A3
- B
- C

If i click to A, the menu is not expanded .. and i don't see A1 A2 A3..

The only way to see them is to set "Expand all children of this tree" to checked in the configuration menu block ..

Someone can help me ?