PHP error: DOMPDF_Internal_Exception: Frame not found in cellmap

When attempting to use the Print PDF function on nodes that include tables, this PHP fatal error occurred:

DOMPDF_Internal_Exception: Frame not found in cellmap in Cellmap->get_spanned_cells() (line 227 of /var/www/gsanetwork.org/public/sites/all/libraries/dompdf/include/cellmap.cls.php).

I did some research and found this GitHub issue in the dompdf project, which includes the suggestion of adding this CSS:

table
{
   border-collapse:unset;   
}

After adding that to print/css/print.css, the error stops and I'm able to generate PDFs of pages that include tables.

This adjustment is needed for both the 7.x-1.3 and 7.x-2.0 versions of the Print module, so I've uploaded patches for each here.