That's because the story is the same the world over. Sorry to sound world weary but this is what all modern corporates do. They follow the letter of their silly rules, designed to save money.
My daughter fell foul of terms & conditions way down hidden in the small print etc. of the Flybe website
She bought a return trip to LGW but the decided that she should get an earlier flight so she bought another ticket.
At the end of her visit she found out at LGW that her return was cancelled due to noshow on the first leg.
In spite of protest she was forced to buy anothe ticket for the return leg.