Winter Soldier: Thank you, comrade— for coming here in person to tell me of your forthcoming marriage. We were sweethearts. Now we are not. It’s a great honor to marry a test pilot hero of the Soviet Union.
Natasha: Yes, comrade Winter Soldier.

Some follow up to this question and this scene. Winter Soldier’s attitude towards Natasha’s impending marriage is completely different here than in the Captain America scene, but I don’t think either is necessarily wrong. The man in this scene is very dutiful Soviet automaton (everyone is named comrade!!), the man in the other flashback is reminiscent of the real Bucky Barnes. It’s not hard to imagine that his personality’d change depending on how well he was overcoming his programming.

But we’ll probably learn more in the upcoming Captain America & Bucky #624.

From Black Widow: Deadly Origin #2, by Paul Cornell and John Paul Leon.