> Legally that land still belongs to Serbia and that comes from last legal border agreement between two sides which is constitution document of Yugoslavia dating from 1974.

That was my initial thought also. One side proposed a new border, and the other side didn't accept. That does not mean it's free land; that means that the status quo continues.

It seems to me the moral equivalent of offering $1 for a house, being rejected, then thereby claiming it's free for the taking...