I'm not entirely sure that is a bug, but it certainly feels like it shouldn't be in the game.
Lately I have been encountering more often planets where the spice buy price is cheaper then the sell price by a large margin. I don't know if it's also possible for other goods, I only encountered this for spice so far.
This makes it possible to buy a full cargo of spice and sell it right away at the same planet. Then you can just rebuy the amount you sold and sell it again. Since you never leave the exchange the prices and amounts never change and you can do this unlimited amount of times. I tested it for a full ingame year with success.
With a large enough difference this makes it very cheap, easy, quick and limitless profits. This makes it possible for even low level star traders to earn millions without having to risk their life or ship in space.
I'm playing the Elite version on Android with a Samsung Galaxy.