mnewton errors out on its own example

Hi,

just a short bug report about mnewton

%i1) load(mnewton);
(%o1)         /usr/share/maxima/5.22.0/share/contrib/mnewton.mac
(%i2) mnewton([2*a^a-5],[a],[1]);

Improper argument to coefmatrix:
(2.0 transpose(h ) + [ - 3.0 ])
                1
                               1
#0:
solve_by_lu(eqs=(2.0*'transpose(h[1])+matrix([-3.0]))[1],vars=
[h[1]],field=complexfield)(mnewton.mac
line 51)
#1: mnewton(funclist=[2*a^a-5],varlist=[a],guesslist=[1])
(mnewton.mac line 113)
 -- an error. To debug this try: debugmode(true);

Since mnewton([2*a^a-5],[a],[1]) is part of the examples for mnetwon 
in the documentation, I guess there is probably some regression.

Note that 

mnewton([2*a^a-5,x],[a,x],[1,0]);

i.e. adding a dummy variable works.

Sergio