It can be kind of annoying. The way I get around it is I click the plus sign to add it to my deck, I go to the deck side mouse over it there, then I can move my mouse straight down to the card without worry of anything getting in the way.
The other way you can get around it is to type in the name of the card you're looking at in the search box. That way only that card is displayed so no other cards will get in the way.
I personally think my way is easier though.