Cannot fix the total magnetization to an odd value?

Created by: twesterhout

It seems that something's wrong with MC sampling for odd magnetizations. Example config:

{ "Optimizer": {"Name": "AdaMax"}
, "Hamiltonian": {"Name": "Heisenberg", "TotalSz": 1}
, "Graph": {"Dimension": 1, "Name": "Hypercube", "Pbc": true, "L": 5}
, "GroundState": {"OutputFile": "test", "Diagshift": 0.1, "NiterOpt": 20, "UseIterative": true, "Nsamples": 2000.0, "Method": "Sr"}
, "Machine": {"Alpha": 2, "Name": "RbmSpin"}
, "Sampler": {"Name": "MetropolisHamiltonian"}
}

netket executable then terminates with the following error:

Cannot fix the total magnetization

It looks like a bug to me, because clearly 5 spins can have a total magnetisation of 1. Am I missing something here?