ZMatrixFactory yields a z-mtrix with a missing atom

[antonio1151]

Dear Sirs,

I am trying to use the function ZMatrixFactory.build_naive() to generate a z-matrix. The system I am using has 728 atoms when I use the function to generate the z-matrix, the sum of the length of the fixed atoms and the z-matrix is not equal to the number of atoms. I was wondering if you could help me with this.
I made the call like this
z_matrix, fixed = bg.ZMatrixFactory(dataset.topology, cartesian=atoms_backbone).build_naive()