There is an inconsistency in ReflectionSymmetry on whether a scalar can have a tensor parity tag that isn't unity (pseudoscalars). In ReflectionSymmetry's apply.c, a scalar GF's tensorparity flag is taken into account, while in interpolation this is ignored. In the ET Toolkit, this only effects those using the ET version of WeylScal4 since only Psi4i, Psi2i, and Psi0i have all been registered as scalars with tensorparity=-1. When interpolating, e.g. Psi4, onto a sphere for mode decomposition, the interpolated quantities have sign errors in Psi4i and give erroneous gravitational wave modes.
This problem applies to both Maxwell release and current development branch. Symptoms reported to me by Jim Healy. I would suggest backporting the resulting fix to Maxwell.
Either ReflectionSymmetry's interpolation has to allow for tensorparity=-1, or apply.c's acceptance of tensorparity=-1 should be removed and WeylScal4's GFs reverted to manually specified parities.