The ECtHR’s inadmissibility ruling in Mansouri v. Italy underscores the enduring tension between procedural formalism and substantive human rights protection in the context of migration control. While affirming Italy’s jurisdiction over the applicant’s confinement aboard a private vessel, the Court dismissed the claim for failure to exhaust domestic remedies, without sufficiently addressing the structural barriers to accessing those remedies. This commentary critically examines the Court’s strict application of Article 35 ECHR and its reluctance to engage with the legal implications of de facto detention carried out by private actors under state instruction. The judgment reflects a formalist adherence to subsidiarity that overlooks the complex realities of contemporary return practices and the legal grey zones they produce.