Going to the front and slowing down to try to control the pace early is a strategy sometimes employed by kickers. Lagat has done this many times and there is nothing wrong with it.
But moving into different lanes (or moving out as Merga has done to Lagat to deny him of perhaps 2 medals) to obstruct someone is a violation of the rules. If I was your coach, I would file a protest, and perhaps talk to the opposing coach about the issue. Your coach can also talk to the officials before the event and ask them to be aware of the obstruction issue.
There is a way of dealing with people like this which is not painless to the obstructor. Go out and attempt to go around the guy, like move into another lane. If he cuts in front of you, get RIGHT behind him (leave no space) and MAINTAIN YOUR PACE. Expect that he will slow down in front of you, and when he does this step on his heels and trip him.