Fellow monks: I am getting some behaviour that appears impossible to me. I have a script that is producing an Excell spreadsheet as follows:

    # Send the last table in a form that Excel can use
    my($quest) = @_;
    my $buffer = "";

    my $fh = new IO::Scalar \$buffer;
    my $book = Spreadsheet::WriteExcel->new($fh);
    my $sheet = $book->add_worksheet("data");

    my %formats;

        ...Removed Code adds some formats with calls like...
        foreach my $f (list_formats())
          {
            my $format = $book->add_format();
            $format->set_bg_color('yellow')
                             if($f =~ /yellow/i);
            $formats{$f} = $format;
          }

    for(my $y=0;$y<=$#last_table;$y++)
      {
        for(my $x=0;$x<=$#{$last_table[$y]};$x++)
          {
            my $val = ${$last_table[$y]}[$x];
            my $format_name = "cell";

               ...Work out the format name...

            my $r;
            $r = $sheet->write_string($y,$x,
                           $val,$formats{$format_name});
#            $r = $sheet->write_string($y,$x,
#                           "$y,$x: Test "."1234567890"x30,
#                           $formats{$format_name});
          }
      }

    $book->close();
    return $buffer;
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As written the resulting spreadsheet will not open in Excell. If I grab only the first 136 characters of the string it works, if I send a long string (as shown in the commented out section) it works.

I have dumped the $val text out and there are no wide characters in it (i.e. it only contains bytes in the range 0x20-0x7A. I have written the data directly to a file (rather than via an IO::Scalar) and it behaves the same.

What is going on? What have I missed?