My educated guess would be there their outsourced and clueless IT guys in India just made a mistake in implementing the booking website.

There is an algorithm in place which determines for which fare type VALUE is shown in the booking process. Those guys have just forgot that codeshares must be included in the algorithm, as well.

For GOT-TXL-ARN it is Air Berlin who is compensating AY Plus for crediting miles/points according to a set earning table. Those IT guys forgot to consider that earning table.