Weird parentheses

[David Sumbler]

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\version "2.19.81"

\language "english"

#(define ((time-parenthesized-time up down upp1 downp1 upp2 downp2)
grob)
   (grob-interpret-markup grob
     (markup #:override '(baseline-skip . 0) #:number
       (#:line (
           (#:center-column (up down))
           #:vcenter "("
           (#:center-column (upp1 downp1))
           #:lower 0.5 "+"
           (#:center-column (upp2 downp2))
           #:vcenter ")" )))))

\new Staff {
  \override Staff.TimeSignature.stencil = #(time-parenthesized-time
"21" "8" "12" "8" "9" "8")
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

A few months ago, when I wrote the file of which the above is a small
part, it worked well, giving the required "21/8 (12/8 + 9/8)" time
signature.

Now, when I compile the file, I get an empty rectangle where the
parentheses used to be.  Furthermore, if I substitute other characters
for the parentheses I get weird results: for instance, a lower case
letter generally gives a capital letter 3 places later in the alphabet
(e.g. "a" appears as "D").

I find though that the letter "p" appears as the dynamic "p".  Perhaps
there is a clue here as to what is going on, but I can't figure it out.

Any suggestions?

David