You'd think that but West Ham seem more than happy to do business with league rivals. They have been pretty much ever since those owners got in. It's all about the money for them 3 I don't think they really understand football that well.
He walks back into the west ham side, the owners are basically still paying off the Haller transfer fee so probably had all this arranged when the initial loan move happened. Sad for West Ham fans though he was probably their most exciting prospect.