It's interesting to read other people suffering from their team not being able to defend crosses.
I'm playing as Luton in the BSP and I'd guesstimate at least 50% of my goals conceded in the league are from crosses. As described above, it usually involves a cross to the back post with an opposition player completely unmarked and a defender actually moving away from the open player.
The inability of fullbacks to deal with wingers is also very frustrating. I have yet to see a full back even block a cross.