You are part of a federation as far as I can tell, the federation tax applies. The same would happen for a Dyson Sphere too, it'd give you 3400 instead of 4000 energy when finished - I'm guessing it's rounding down instead of up and so displaying 1 when the value is closer to 2. Or maybe it's truncating, in which case yes it ought to be a bug - but please do check exactly how much you get from the deposit once you build a station over it.
Edit: i.e. I've seen this happen every time with energy deposits when I'm part of a federation, I just never bothered to check whether it legitimately reduces by a whole one energy or just a fraction because usually the contribution is largely insignificant at that point.