\hline in array creates empty row

[xworld21]

The following simple array

\[ \begin{array}{c|c}
  a & b \\
  \hline c & d
\end{array} \]

creates an extra empty row with border t, instead of adding border="t" to the cells below (or border="b" to the ones above, whichever is more accurate). Moreover, the empty row does not respect the c|c specifier, in the sense that the vertical border is missing.

I guess that maybe this is done because if there aren't enough many cells, the horizontal line won't span the entire table (?). If that's the case, wouldn't it be better to pad the current (or previous) row with the missing cells? As it is now, LaTeXML creates a rather ugly empty gap. It looks even worse when fed through MathJax.