I just took a peek at the source of the latest Spreadsheet::TieExcel on CPAN (0.73). It executes $\ = "\n"; $, = "\t";. It doesn't even use either of these vars, directly or indirectly, as far as I can tell.

The workaround is to change

use Spreadsheet::TieExcel;
[download]

into

BEGIN {
   # Prevent Spreadsheet::TieExcel from clobbering $\ and $,
   local ($\, $,);
   require Spreadsheet::TieExcel;
   Spreadsheet::TieExcel->import();
}
[download]