Problem with the null space

I have the following matrix:

X=[0 0 0 0 0 0 0 0 -146 -80 -258 -134 -11 -215 5 -119;

0 0 0 0 -146 80 258 -16 0 0 0 0 48 -156 64 -60;

0 0 0 0 -11 215 393 119 48 114 -64 60 0 0 0 0;

146 -80 258 254 0 0 0 0 0 0 0 0 183 -21 199 75;

11 -215 123 119 0 0 0 0 -87 -21 -199 -75 0 0 0 0;

-48 -274 64 60 -205 21 199 -75 0 0 0 0 0 0 0 0];

When I calculate the a rational basis of the null space with null (X, 'r') and apply X * null (X, 'r') I get the matrix:

[0 0 0 0 0 0 0 0 -0.0000 0 0;

0 0 0 -0.0000 0.0008 -0.0029 0.0001 0.0003 0.0014 -0.0015 0.0012;

0 0 0.0000 0 0.0048 -0.0005 -0.0005 0.0008 0.0003 0.0001 0.0043;

0 0 0 0 -0.0006 0.0003 -0.0006 0.0006 0.0002 0.0015 -0.0019;

0 0 0 0 0.0001 0.0011 -0.0003 0.0008 0.0002 0.0037 -0.0004;

0.0000 -0.0000 0 0 -0.0007 -0.0025 0.0002 0.0011 0.0020 0.0023 0.0001]

which is clearly not zero. Something is wrong here. On the other hand, if I work with the reduced row echelon form, I do get the zero matrix when computing rref (X) * null (X, 'r'). The RREF matrix has the same null space as the original matrix X. Why does this difference occur in the result?