A couple of months ago Sebastian Stan, the actor who plays Bucky Barnes in Captain America: The First Avenger, will return as the Winter Soldier in next years sequel. Stan Talked to Empire about his return. He said "...We have to freeeze the rescue scene when captain america comes to get him back." I've watched the scene in Movieclips.com and I have discovered something:
As you can see, there is machine pointing at his head. I guess that Arnim Zola brainwashed him. Even Steve Rogers looks at the machine:
I know it's not a very good quality set of images, however, it's all there. I have also noticed that Bucky is speaking Russian when Steve arrives and that he had a silly face, acting and speaking strangely. I am starting to think, since that moment, he was already brainwahed. He might have already been converted to the early Winter Solider... Falling from that train was part of his plan and he wanted to do that.
This is my theory, and here is the clip, tell me your opinions.