do_free='z' does not work properly for BFGS

Hi QE community,

When I set do_free='z', the behavior is not as described in the documentation when using BFGS (as of v6.3). Specifically, I would expect, as per the documentation, that the z component of only axis 3 be free to move. This, however is not the case, and the component of all axis are able to move when I set do_free='z'.

However, when I run with cell_dynamics='damp-pr' (the default for cell_dynamics is 'bfgs'), the system relaxes as specified in the documentation, the z component of only axis 3 is free to move.

I've linked sample inputs/outputs that demonstrate this behavior.