cat does not convert sparse matrices?

[Francesco Potorti`]

In Octave 3.0.1, I cannot catenate a full double matrix with a sparse
logical matrix.  Is this normal or a bug?

octave> a=zeros(3,3,0);
octave> b1=zeros(3,3);
octave> b2=sparse(1,1,true,3,3);
octave> whos a b1 b2

*** local user variables:

  Prot Name        Size                     Bytes  Class
  ==== ====        ====                     =====  ===== 
   rwd a           3x3x0                        0  double
   rwd b1          3x3                         72  double
   rwd b2          3x3                         21  logical

Total is 10 elements using 93 bytes

octave> size(cat(3,a,b1))
ans =

   3   3   1

octave> size(cat(3,a,b2))
error: invalid conversion of NDArray to Matrix
error: range error for insert
error: evaluating argument list element number 1

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