convert-ly not handling footnotes correctly

[Nick Payne]

In 2.15 I had footnotes set out like so:

\version "2.15.35"

\relative c'' {
    c4 c-\footnote #'(0.7 . 2) #'NoteHead \markup\teeny { Automatic footnote }
    c c-\footnote "a)" #'(0.7 . 2) #'NoteHead \markup\teeny { \concat { \lower #0.8 \super { a) } "Manual footnote" } }
}

With 2.15.35 this builds without error and gives correct output. Running 2.17.7 convert-ly against it changes the source to that below, without any warning messages on the console, but trying to build the file gives a couple of error message on the console: "programming error: Not a music type", and the footnotes are missing from the output.

\version "2.17.6"

\relative c'' {
    c4 c-\footnote #'(0.7 . 2) \markup\teeny { Automatic footnote } NoteHead
    c c-\footnote "a)" #'(0.7 . 2) \markup\teeny { \concat { \lower #0.8 \super { a) } "Manual footnote" } } NoteHead
}

Nick