Skill cards are mixed within the rest of the deck

IIn a speed duel room, skill cards are not played as such but remain mixed in with the rest of the deck. In case some are drawn and played they end up in the graveyard without any effect. Are there problems with the way I build decks/create rooms to play speed or is this a problem with the game?

The skill cards I have used so far are all from the original speed duel set, no custom cards nor from duel link.

Ca somebody help me? Thx