It sounds like the magnetic field is somehow interacting with the photon/nucleus/electron absorbtion/re-emission. The photons don't feel the magnetic field, but

It sounds like the magnetic field is somehow interacting with the photon/nucleus/electron absorbtion/re-emission. The photons don't feel the magnetic field, but the combined system appears as if they do? It's like how light appears to slow down in a material: it isn't actually slower, but the photon re-emission makes it appear so. (not a physicist)