I think they score a bit less than they should, also playing with Utd, have Rooney, Lukaku and Reus as main PK takers (in that order of preference) and I had a period where I missed 5 out of 6 penalties, then scored and haven't had another awarded since (about 9 games or so).
what makes it more unrealistic is the AI have never missed one against me, despite their players being inferior in terms of stats for composure, penalties, technique, decisions etc and DDG being better than their 'keepers.
It's not an earth shattering bug, but I think it needs tweaking.