Partial trace over symbolic matrix

I want to perform the partial trace over a symbolic matrix that contains fractions , for example:

N_sym=sym(1/32*eye(8));

Which is:

N_sym =
 
[ 1/32,    0,    0,    0,    0,    0,    0,    0]
[    0, 1/32,    0,    0,    0,    0,    0,    0]
[    0,    0, 1/32,    0,    0,    0,    0,    0]
[    0,    0,    0, 1/32,    0,    0,    0,    0]
[    0,    0,    0,    0, 1/32,    0,    0,    0]
[    0,    0,    0,    0,    0, 1/32,    0,    0]
[    0,    0,    0,    0,    0,    0, 1/32,    0]
[    0,    0,    0,    0,    0,    0,    0, 1/32]

So my code would be

N_sym=sym(1/32*eye(8));
sys=[1,2]; % Defines the subsystems that I want to trace out
dims=2*[1 1 1]; % Defines the dimensions of each subsystem
PartialTrace(N_sym,sys,dims) % A function in Qetlab (http://www.qetlab.com/PartialTrace)

and I get the following message:

Error using symengine
Arguments must be 2-dimensional.

Error in sym/privUnaryOp (line 1019)
            Csym = mupadmex(op,args{1}.s,varargin{:});

Error in sym/sum (line 55)
    s = privUnaryOp(A, 'symobj::prodsumdim', num2str(dim), '_plus');

Error in PartialTrace (line 93) % If you click on "(line 93)" the source code will pop-up
        Xpt = sum(Xpt(:,:,1:sub_sys_vec(1)+1:sub_sys_vec(1)^2),3);
        

Seems that there is some problem with the fact that I (partially) trace a symbolic matrix, although in the source code (see comment on the code above in order to see the source code) seems to be considering the case of a non-numeric matrix... Let me know if something needs to be clarified more!

Any ideas how to make it work? Any hint will be of great help!!

Thanks!