When using the default setting (layer 1 set only) nothing is stored in the tscn file for a Light2D, hence it relies on the value in the constructor.
The problem is the constructed value is 1 in Light2D, and -1 in RasterizerCanvas::Light. -1 results in all bits being set so all occluders are shown, rather than just those in layer 1.
This PR changes Rasterizer::Canvas constructor to set to 1. An alternative is to have -1 as the value for layer 1 throughout.
bf54fa5a62