Inconsistent results for Script Y-offset

[Marco Caliari]

> I'm not top posting.

Dear all, 

in the following snippet

\version "2.11.52"
\relative c' {
\time 6/8
f4. f4 f8(
\once \override Script #'Y-offset = #4
% no effect
d'4.-> ~ d4.)
f,4. f4 f8
\once \override Script #'Y-offset = #4
% desired effect
d'4.-> ~ d4.
f,4. f4 f8(
\break
\once \override Script #'Y-offset = #4
% strange effect
d'4.-> ~ d4.)
}
\paper{ ragged-right=##t } 

the \override Script produces inconsistent results (the last one quite bad).
Finally, I found that I have to override the padding property: still, I think
there is something wrong with #'Y-offset.

Best regards,

Marco