Chrome bug : extra unrequested border in table

The comparison map into the fibre product, i.e., pullback
$\homst \setX \Set \setY \longrightarrow \source(\symsX \source\backslash \homst \setX \Set \setY\source) \times_{(\symsX \source\backslash \homst \setX \Set \setY \target/ \symtY)} \target(\homst \setX \Set \setY \target/ \symtY\target)$
when $\source{(\setX=[4]=\{0,1,2,3\})}$ and $\target{(\setY=\{\elta,\eltb\})}$

$\SetXY \rlap{\target{{} \xrightarrow[\mkern28em]{\displaystyle t} {}}}$							$\homst \setX \Set \setY \target/ \symtY$
	$\elta^4$	$\eltb^4$					$0123\mid{}$		$4+0$
$\smash{\llap{s}\Bigg\downarrow}$			$\elta^3\eltb$	$\eltb^3\elta$			$012\mid3$		$3+1$
			$\elta^2\eltb\elta$	$\eltb^2\elta\eltb$			$013\mid2$
			$\elta\eltb\elta^2$	$\eltb\elta\eltb^2$			$023\mid1$
			$\eltb\elta^3$	$\elta\eltb^3$			$123\mid0$
					$\elta^2\eltb^2,\eltb^2\elta^2$		$01\mid23$		$2+2$
					$\elta\eltb\elta\eltb,\eltb\elta\eltb\elta$		$02\mid13$
					$\elta\eltb\eltb\elta,\eltb\elta\elta\eltb$		$03\mid12$
$\begin{array}{} \symsX \source\backslash \homst \setX \Set \setY\\ \displaystyle \bigg(\mkern-.35em {\target{{\setY=\{\elta,\eltb\}}} \choose \source{|\setX|=4}} \mkern-.35em\bigg)\\ \end{array}$	$\begin{array}{}4+0\\ \elta^4\\\end{array}$	$\begin{array}{}0+4\\ \eltb^4\\\end{array}$	$\begin{array}{}3+1\\ \elta^3\eltb\\\end{array}$	$\begin{array}{}1+3\\ \elta\eltb^3\\\end{array}$	$\begin{array}{}2+2\\ \elta^2\eltb^2\\\end{array}$
	$4+0$		$3+1$		$2+2$				$\symsX \source\backslash \homst \setX \Set \setY \target/ \symtY$