clef changes

[Giammarco Zacheo]

While writing piano parts I got a small problem when a clef change occurs 
at the end of a bar:
if there is a clef change i.e. a clef change to bass in the lower staff, an 
extra space appears in the upper staff;
this does not happens when the clef change occurs in the middle of a bar. 
Sometimes in this case the clef is
too close to the preceding note.
How can I override this? I am really not an expert lilypond user, so...

Thanks & Bye

Giammarco