Disklavier

I recently moved from a worn down baby grand (bad shape) to a U1 
Disklavier upright.  

The upright has that ledge on two hinges secured to the underlide of 
the keyboard lid.  The ledge is to support the music.  Unfortunately, 
it cannot support heavier books....ie my favories "Fake 
Books"....because of the weight.  The ledge simply slips down.  

Is this a common problem?  A dumb design?  Or is my question just 
silly?  I guess I just have to rip pages out of the Fake Book, or even 
other song books, when this happens?  

Geoff