Factoring matrix expressions, even trivial ones?



Is there any way for Maxima to factor 'a' back out of a*M, as below?

Maxima 5.28.0-2 http://maxima.sourceforge.net
using Lisp GNU Common Lisp (GCL) GCL 2.6.8 (a.k.a. GCL)
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) M:transpose([x,y]);
                                     [ x ]
(%o1)                                [   ]
                                     [ y ]
(%i2) a*M;
                                    [ a x ]
(%o2)                               [     ]
                                    [ a y ]
(%i3) %,factor;
                                    [ a x ]
(%o3)                               [     ]
                                    [ a y ]
(%i4) ????