\midi broken in conjunction with non-plain voice contexts

[Jürgen Reuter]

Hi,
as of current cvs head, the following snippet:

\version "2.9.10"
\score {
    \new CueVoice = "test" {
        c d e f
    }
    \midi {
    }
}

results in the following error message:

warning: can't find or create new `CueVoice'

If I comment out the \midi block, the snippet compiles fine.  I also get similar
messages if I use TabVoice or VaticanaVoice instead of CueVoice.  Only Voice
seems to work fine.

Greetings,
Jürgen