Issue with DynamicTextSpanner style override

[Olexa Bilaniuk]

> I'm not top posting.

While trying to create a custom crescendo in LilyPond 2.13.59 and 2.12.3, I came
up against what I believe is a bug in DynamicTextSpanner's style override : When
I set 'style to 'hairpin, what is printed out is a straight line, identical to
the result of setting style to 'line, or anything other than dashed-line or
dotted-line for that matter. The code that triggers the bug here is lifted (save
for the change to 'hairpin) straight from Snippets -> Expressive marks ->
Changing text and spanner styles for text dynamics, and though the description
claims that 'hairpin is a valid style, it clearly is not here. Erroneous output
is in red.


\version "2.13.59"

\relative c'' {
  \set crescendoText = \markup { \italic { cresc. poco } }
  \set crescendoSpanner = #'text
  \override DynamicTextSpanner #'style = #'line
  a2\< a
  a2 a
  a2 a
  a2 a\mf
  \once \override DynamicTextSpanner #'color = #red \override DynamicTextSpanner
#'style = #'hairpin
  a2\< a
  a2 a
  a2 a
  a2 a\mf
}