Using latest Moodle and latest DragMath and latest Java on latest Firefox and Safari and this:
$$ \left( \begin{array}{ccc} {a} & {b} & {c} & {d} & {e}\\{f} & {g} & {h} & {i} & {j}\\ \end{array} \right) \times \left( \begin{array}{ccc} {k}\\{l}\\{m}\\{n}\\{o}\\ \end{array} \right) $$
produces a matrix image that has only 3 columns, with the 4th and 5th column elements wrapped into the next row.
It does the same thing with any matrix with more than 3 columns.
example of 2X5 improperly displayed