hist3 not returning expected output

I was trying to use hist3 to visually display a two-dimensional distribution, however the function behaves unexpectedly. I thought that it returns a 2D histogram (a count) of how many times each pair of numbers in the input matrix occurs, and displays that count at a position in the output matrix whose indices correspond to that number pair, scaled to a factor of 10 (by default) or some other square-matrix size. But this is not what my test examples showed.

If I define the following input matrix

1  1
2  2
3  3
4  4
5  5

then the command

v=hist3(m, [5 5])

has the following output (as expected):

1  0  0  0  0
0  1  0  0  0
0  0  1  0  0
0  0  0  1  0
0  0  0  0  1

However for this input matrix:

4  1
4  2
4  3
4  4
4  5

the output is:

0  0  0  0  0
0  0  0  0  0
1  1  1  1  1
0  0  0  0  0
0  0  0  0  0

..rather than (as I would have expected):

0  0  0  0  0
0  0  0  0  0
0  0  0  0  0
1  1  1  1  1
0  0  0  0  0

Can anyone help clear the confusion? THanks!