Oh I See What Your Trying
THIS IS NOT A BUG
Remember the thumb image returns a link to the category it is in.
If you want to have it link elsewhere you need to place an ahref tag around the thumb to link to the product.
You where the very one weeks ago reporting an extra <a href tag which had me remove exactly what your trying to do
The link should be this then
if ( $Globals['spider'] == "yes" ) $gallery['hasimage'][$count] = "<a href=\"{$Globals['maindir']}/showproduct.php/product/$id/sort/$sortparam/cat/$cat/page/$page\">$thumbrc</a>";
else $gallery['hasimage'][$count] = "<a href=\"{$Globals['maindir']}/showproduct.php?product=$id&sort=$sortparam&cat=$pcat&page=$page\">$thumbrc</a>";