If you're asking for you to choose the cards, is not the way it works in PTCGO. The word RANDOM in the PTCGO means the game will choose for you, as it's random, who cares.
Is not like IRL, opponent could have the hand cards ordered left to right as Pokémon > Trainers > Energies, and you choose the hand on one side or another trying to remove the most important things. As revealed, you could figure the order of opponent's had for next moves, although the smart move from opponent would be to shuffle the hand before you choose to make it more random.
Also in PTCGO, in your hand you see the cards ordered (and you can vary this order in Settings) but what you see in opponent's reverse cards is not the same. For you the order is also random. If there are 3 cards, Pokémon-Trainer-Energy ordered for opponent, choosing the middle one doesn't ensure being the trainer. That's tested.
So at the end claiming Heads and only 1 card discarded, it's a bug.
But at the time to make you choose the cards, doesn't care if you pick it or game just choose, as everything would be made random anyway and this is probably, working as intended.
WE WANT LEGACY TOURNAMENTS BACK !!! If you also want it, show your support http://forums.pokemontcg.com/topic/55966-feedback-making-it-easier-to-get-the-cards-you-want/
My 1st pokémon VGame http://forums.pokemontcg.com/topic/59894-my-1st-pok%C3%A9mon-videogame-nds-diamond-story-and-help/
Foro en español, también existe: http://forums.pokemontcg.com/forum/2-español/