PDF to reduced size PDF, mangles fonts after 50 pages

I sometimes use PDF Creator to reduce the size of lectures posted on class web sites.  They come to me as PDF, and are printed from PDF Xchange viewer (2.0 build 44) to PDF creator (0.9.5)  to make the final file smaller.  The (original) pages look normal in the viewer, but those in the smaller file have mangled text after some point..  The print dialog (and sub menu) options are:

    print all pages
    paper size 1024 x 768 (XGA)
    150 dpi
    fit to printer margins
    auto center

In PDF Creator the dpi is set 150 for the various PDF image settings.  This generally works.  However, for very long files, for instance with the following 50 page file (this is the original, without the corruption - 25MB!)


it goes wrong, here at at page 49, with the text all messed up.  The images are fine on pages where the text is not.

Anybody know what is going wrong and where?  Is this a PDF Xchange viewer issue, a PDFCreator issue, or a ghostscript issue?


Possibly related observation.  Running a page extraction on linux like this on the problem file

gs -sDEVICE=pdfwrite \\-dNOPAUSE -dBATCH -dSAFER -dFirstPage=48 -dLastPage=48 -sOutputFile=out.pdf  BMB170c_2010_LECTURE11.pdf

Results in these messages:

GPL Ghostscript 8.64 (2009-02-03)
Copyright (C) 2009 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
   **** Warning:  File has an invalid xref entry:  22.  Rebuilding xref table.

Processing pages 1 through 1.
Page 1

   **** This file had errors that were repaired or ignored.
   **** The file was produced by:
   **** >>>> Mac OS X 10.5.8 Quartz PDFContext <<<<
   **** Please notify the author of the software that produced this
   **** file that it does not conform to Adobe's published PDF
   **** specification.

However, the output file looks OK.  Possibly because this ghostscript command seems to have converted it to an image, whereas with PDF-Creator it seems to retain its text/fonts.  (But maybe gets some index out of whack?)