Syntax for make-dynamic-script

[Richard Shann]

Can anyone spot what is wrong with this?
 
\version "2.16"

MvmntIVoiceI = {
        <>  #(make-dynamic-script (markup #:normal-text #:bold #:italic 
"pia."))  a'4 
}

\score { 
          \MvmntIVoiceI         
}

It is supposed to place a customized dynamics "pia." on the score. It
does this, but the point-and-click location given is
textedit://filename:0:0:0

that is, no line or column information. Curiously, if I insert the text
of the definition directly, all is well.

Richard