Is this supposed to work as such? I was hit by entangling roots and even though I was standing next to an opponent I could not use step attacks. I understand that I can't move but should I not be able to attack in place?
This sounds like normal functionality. I had a similar thing happen to me when my priest had the polearm weapon that doubles as armor, and lost it when someone used a dissolve armor spell on her. The card is seen by the game as both movement & attack. Similarly the polearm is seen as both attack & armor. So when the entangling roots doesn't allow you to play movement cards, it sees those as movement as well. I'm not an expert, but that's my 2 cents.
Right which sounds off. Not like a bug but overlooked. Normally if you wanted to use a step attack you don't have to move to use it, you stand still change your facing and attack. Since entangling roots prevents movement it should not prevent the attack part of that card.
But 'halt' doesn't prevent the character from moving, but rather it prevents them from playing move cards. So my impression is that it's deliberate and intended. On a somewhat related note though, apparently step cards count as a subtype of move cards for the purpose of halt, but not for Pathfinding. Both of these things only mention move cards, and so it's inconsistent that one should include steps and not the other. (I'm not completely certain about this, and I can't check it right now because the server is down. So please correct me if I'm wrong.)
Yes, this is normal and intended. As other have said, hybrid cards count as both types of cards. If you can not play move cards, you will not be able to play hybrid move/attack cards.
This is working as intended. Pathfinding should draw step cards - if not, please report this as a bug!