Bare durations as music function argument?

[Simon Albrecht]

Hello,

the bare durations that can now be used to write notes with unspecified 
pitch don’t work as music function arguments:

\version "2.19.32"
\new DrumStaff \with {
  \override StaffSymbol.line-count = 1
} \new DrumVoice {
  4 \slashedGrace 16 4
}
\relative {
  r4 r8 c'' \appoggiatura 4 b2
}

– each yielding ‘error: wrong type for argument 1.  Expecting music, 
found 16’ or similar.

David, is that intentional?

Yours, Simon