Tie/slur bug in 2.9.11?

[John Wiedenhoeft]

When I try the following:

\version "2.9.11"

erga = {\once \override NoteHead #'style = #'diamond a}
para = {< \parenthesize a>}

{
a ~ \erga ~ \erga 
a( \erga) \erga( a)
a ~ \para ~ \para 
a( \para) \para( a)
}

I get:

GNU LilyPond 2.9.11
Processing `greg.ly'
Parsing...
greg.ly:7:10: error: syntax error, unexpected '~'
a ~ \erga
          ~ \erga
greg.ly:8:8: error: syntax error, unexpected ')'
a( \erga
        ) \erga( a)
greg.ly:9:10: error: syntax error, unexpected '~'
a ~ \para
          ~ \para
greg.ly:10:8: error: syntax error, unexpected ')'
a( \para
        ) \para( a)
greg.ly:6:0: error: errors found, ignoring music expression

{
error: failed files: "greg.ly"


I can't see whats wrong. Should I forward this to the bug reports?

Cheers,
John