Basically when you hit W for Pick a Card it begins the card selection cycle. If you are currently auto attacking and "Pick a card" in the middle of the attack animation, he will stop attacking. Not sure what can be done about that since I assume this is because he is being given another command instead of attacking. I think a good fix for the first part is to have him continue to throw a normal card, and then throw the picked card after. Or have him throw the picked card no matter where in the attack animation he currently is.
The second part is after the Picked card is thrown. There is a noticeable 'stop' in attacking. This is easily seen if you have significant attack speed, because you can notice immediately that he stops attacking longer than the typical pause between attacks. This is alleviated by moving immediately after the card is thrown, which is what most of us cardmasters do. But in doing so we lose the time that we could have been attacking.
Still not 100% on the wild card problem I mentioned, I would have to extensively test it to really figure it out. It seems to only miss on moving targets, so obviously there is the possibility I could be missing them. It is difficult to determine because the cards are so small (which I understand of course they are playing cards). However it seems that they hit for a larger AOE than the graphic is. If that is the case than I'm sure they don't damage occasionally.
I'll do some extensive testing to give more accurate feedback regarding the Wild Cards.
Well from what I can tell the Wild Cards don't hit outside of the graphic, I was confusing that with grazes which do inflict damage. I did however notice a 'stop' after the Wild Cards are thrown as well.