LabelType Centered_Top_Environment Doesn't Seem to Center

[Alexander M. Budge]

I would like to add a static label, centered above the user supplied
text.  Everything seems to work fine with the snippet below, except
the label "Short Title:" is not centered above, but displaced to the
right.

What's going on?

Thanks,
Alex

--------

# Short Title style definition
Style ShortTitle
  Margin                Static
  LatexType             Command
  InTitle               1
  LatexName             setshorttitle
  ParSkip               0.4
  ItemSep               0
  TopSep                0
  BottomSep             1
  ParSep                1
  Align                 Center
  AlignPossible         Center
  LabelType             Centered_Top_Environment
  LabelString           "Short Title:"

  # standard font definition
  Font
    Shape               SmallCaps
  EndFont

  # define auxillary command to set short title
  Preamble
    \newcommand{\setshorttitle}[1]{\gdef\shorttitle{#1}}
  EndPreamble
End