bug or syntax?

[David Bobroff]

inv = {
     \override Staff.NoteHead  #'style = #'transparent
     \override Stem  #'transparent = ##t
     \override Accidental #'style = #'transparent
}

unv = {
    \override Staff.NoteHead  #'style = #'default
    \override Stem  #'transparent = ##f
    \override Accidental #'style = #'default
}

\score {
    \notes {
        c d e f g \inv a \unv b c
    }
}


The above worked fine in 2.1.27 but in 2.1.28 (ChangeLog 1.1794 'release
commit') I get this:

 warning: note head `noteheads-2transparent' not found:
        c d e f g \inv 
                       a \unv b c

Did I miss a syntax change (I did run convert-ly on the file) or is
something broken?

-David