Space between systems in lilypond-book

[Hugo Ribeiro]

Dear all,

When I compile my lytex file with a piano music example, it seems that 
LaTex shrinks the space between systems, so the output is not ok. The 
systems looks too tight.  When I compile only the music example, the 
distance between the system are ok.

Note that I am talking about the distance between the systems, not the 
space inside the system and between the staves.

Any hind?

Thanks,

Hugo