Here's a slight variation on LH pricing quirks but I don't want to start a new thread.

Checking same day return fares in Y for MAN-FRA. On the chosen date a return fare is available at £314 according to the initial grid display.



The next screen shows the price options for the outbound and inbound flights and the lowest fares available are £144.90 and £107.60 respectively. (Incidentally the total of £144.90 and £107.60 is less than £314.)



However, if you actually select any of the outbound or inbound flights, the prices for flights in the other direction suddenly increase and there's no way you can buy a return ticket for £314.

The inbound fare more than doubles if you actually select an outbound flight first...



and if you select an inbound flight first the outbound fare increases by £80. The lowest return fare is still more than £314. Why advertise a fare which is impossible to book?