There were certainly posts here in the past -- now deleted in the purge -- where travellers were unable to enter Serbia proper from Kosovo after entering Kosovo from Macedonia.
And the UK Foreign Office still warns of this issue:
"If you try to leave Serbia without an entry stamp or exit-entry visa you may face charges of illegal immigration, a heavy fine and possible imprisonment. You should only enter Serbia through recognised border crossings. The authorities in Serbia don’t consider the designated crossing points with Kosovo to be official ‘international’ border crossing points. Foreign nationals have been denied entry to Serbia if they have Republic of Kosovo stamps in their passports."
https://www.gov.uk/foreign-travel-advice/serbia/entry-requirements
As does the US State Department:
"Travelers coming to Serbia by land through Kosovo have had problems with Serbian border authorities at checkpoints on the borders between Kosovo and Serbia. Serbian immigration police have refused to accept travelers’ Kosovo entry stamps, claiming that the travelers were in Serbian territory illegally, and refusing to allow them to travel any farther into Serbia."
http://travel.state.gov/travel/cis_pa_tw/cis/cis_1014.html