Question about trigrat & matrices



I want to apply trigrat to the elements of a matrix, for example:

                                                p1:matrix([1,0],[0,-1]);
                                                p2:matrix([0,1],[1,0]);
                                                p3:matrix([0,1],[-1,0]);
                                                S:s1*p1+s2*p2+s3*p3;
                                                M:(ident(2)-coth(del*t/2)/del*S);
                                                trigrat(%);
                                                
However, when I try to run this I get:

(%i6) trigrat(%);
Maxima encountered a Lisp error:

 
CAR: 1 is not a list

Automatically continuing.
To reenable the Lisp debugger set *debugger-hook* to nil.


Is this a bug?  (I'm using a fairly recent CVS version and clisp)

David