Yes I did make sure to finalize the path data before saving the prefab (otherwise the path objects don't get exported at all!)
When I press "alt" to reset the cursor, that doesn't do anything because when the prefab is loaded the cursor automatically gets rescaled to the size of the prefab. So somewhere in the prefab code the origin coordinate calculation for footpath objects is messed up. Copy/pastes seem to be working fine though, so I'm not sure what's causing this