Well, this is a J-3 simulation, which is modeled after the real deal.
As such, it would not be in keeping with the real deal to include any lighting, internal/external. The J-3 has no such thing. There are many good J-3 cub resources on the net that could help you become better familiar with this bird.
And regarding the bug question... I would think that since there is no lighting modeled, I would say with much certainty.. not a bug.
This is a day/VFR aircraft.
I hope that answers some questions you have.
Yeah you are right, this bird is a blast.
I think it's great that it's like the real thing and therefore a pity you can't fly it at night. But it is "as real as it gets".
That said. Press shift+L (the default setting for cockpit light) and the light goes out but then turns back on after about one second. It appears to be automatically on and does not stay off.
This snippet from the aircraft.cfg proves it:
//Types: 1=beacon, 2=strobe, 3=navigation, 4=cockpit, 5=landing
light.0 =4, 1.200000, 0.000000, 1.600000, fx_A2A_J3CUB_vclight
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