That article is referring to http://www.putevi-srbije.rs/pdf/serbia_main_and_regional_road.pdf as source (here is JPG version of the same http://img153.imageshack.us/img153/4853/mapaputeva.jpg). There you can see part of E-80 between Niš and Priština overlaps with E-771, so all wiki articles that say E-771 end in Priština, probably uses same source. Even though this map comes from official site it might be outdated or simply incorrect in some parts.

And something else I noticed, in ref tags, numbers and letters are separated by space. On our wiki page http://wiki.openstreetmap.org/wiki/Serbia#Broj.C4.8Dane_ref.3D.2A_oznake there are no spaces in names but on English E road wiki http://wiki.openstreetmap.org/wiki/WikiProject_Europe/E-road_network#Tags_for_the_relation there are spaces. Further more it says E # ref is assigned to relation not to road, and I saw roads with E number on them selves, is this correct or should be changed.