Custom dynamic vertical positioning

[Andrew Bernard]

When making a simple custom dynamic, a p followed by an em dash, compared to 
the same thing for a p followed by a hyphen, the vertical alignment differs. 
What am I doing wrong, or not understanding? I thought the alignment of the two 
in the same context would be identical.

[I have pasted a unicode character in the code for pEmDashText, since lilypond 
accepts this. I am not sure if it will survive various mailers, but it is 
Unicode 2014.]

Andrew

— snip

\version "2.19.29"

pHyphenText = \markup {
 p \normal-text -
}
phyphen = #(make-dynamic-script pHyphenText)

pEmDashText = \markup {
 p \normal-text —
}
pemdash = #(make-dynamic-script pEmDashText)

treble = {
 \clef treble
 \time 1/4
 c''\p c''\pemdash c''\phyphen c''\p
}

\score {
 \new Staff { \treble }
}

— snip