Piano accidentals don't work in a GrandStaff

[Yuval Harel]

Hello,

The Notation Manual page on Accidentals 
( http://lilypond.org/doc/v2.2/Documentation/user/out-www/lilypond/Accidentals.html#Accidentals) 
reads:
---SNIP---
        piano
		This rule reflects 20th century practice for piano notation. Very 
similar to modern but accidentals also get canceled across the staves in 
the same GrandStaff or PianoStaff.
---SNIP---

But #(set-accidental-style 'piano) does not word at all inside a 
GrandStaff - not even for accidentals on the same staff.
Here is a simple example:
\score {
    \notes \relative c' {
%       \new PianoStaff << % this works fine
        \new GrandStaff << % this does not work fine
            #(set-accidental-style 'piano)
            \new Staff {
                fis1 | f
            }
            \new Staff {
                        c2 f
                }
        >>
    }
}

Thanks,
        Yuval