SystemStartBrace in PianoStaff

[Valentin Villenave]

Hello everybody,

I'm not very talented in Lilypond typesetting but -still- I wonder how
comes the same Pianostaff code can make a "standard" Piano system
Brace :

http://www.mutopiaproject.org/ftp/ChopinFF/O27/chopin-nocturne-8/chopin-nocturne-8-preview.png

or a "small" one :

http://www.lilypond.org/doc/v2.9/input/mutopia/E.Satie/petite-ouverture-a-danser-page1.png

It's something I definitely can't understand ; as far as I'm
concerned, I have a .ly script which goes like this :

\score {
       <<
                 \set Score.markFormatter = #format-mark-box-letters
                 \override Score.RehearsalMark #'break-align-symbol = 
#'staff-bar
        \context Staff = "flute" \flute

               \new PianoStaff <<
                       \context Staff = "upper" \pianod
                       \context Staff = "lower" \pianog
                        \set PianoStaff.instrumentName = "Piano"
                        \set PianoStaff.shortInstrumentName = "Pno. "
                        %%\override PianoStaff.SystemStartBrace #'transparent = 
##f
               >>
       >>
       \layout {}

and I usually get a "standard" Brace ; but since I updated Lilypond to
version 2.9.26, I now get a "small" one.

Can somebody nice tell me more about it ?