When Cyprus joined the EU, it also became part of the system of EU law, though EU law is suspended from the Northern Turkish Cypriot part of the island. But there has just been a ruling that means if EU law doesn't apply there, then it could still apply to EU citizens and their actions in Northern Cyprus.
The BBC has reported that the ECJ has upheld* a Cypriot court ruling (that a villa built by British citizens on land that was owned by a Greek Cypriot before the war with Turkey must be demolished) and stated that court rulings in one member state must be recognised in another. This means that the owner of the land (in the eyes of the Greek Cypriot government), Mr. Apostolides can sue for compensation in the UK courts. Of course the villa in question cannot actually be demolished until (and unless) there is Cypriot reunification.
BBC background story here.
I wonder how this will affect Greek-Turkish Cypriot relations - it will certainly damage whatever market for property investment there still is in Turkish Cyprus. And it could prove another serious block in the peace process/reunification movement: it will probably raise tensions at least, though the victory of the Nationalist Party in the recent elections in Northern Cyprus have already added more strain to Cypriot relations.
*The ECJ can only interpret Community law, which is then applied by the courts in their rulings, so this I doubt it "upheld" the original ruling - it would be more to do with court recognition and compatibility with EU regulations (I'm not sure of the regulations in this area). I would be very interested in reading the ECJ case, if anyone knows the citation for it.
Edit: The Irish Times seems to give a slightly clearer overview.