Summary We present a case series of intra‐operative adverse events while using a specific type of bronchial blocker, designed to facilitate device positioning and minimise the risk of dislocation. The Rüsch® EZ‐blocker™ (Teleflex Life Sciences Ltd., Athlone, Ireland) is a Y‐shaped catheter equipped with two separately inflatable cuffs at the tip – one for each bronchial lumen. In this report, we describe four cases where the use of the EZ‐blocker was associated with the development of high airway pressures, hypoxaemia and expansion of the non‐dependent lung. Bronchoscopic evaluation showed spontaneous inflation of the cuff within the dependent (i.e. ventilated) bronchus, causing bronchial obstruction, and volume loss of the cuff within the non‐dependent (i.e. unventilated) bronchus, causing unintended expansion of the non‐dependent lung. After removal of the bronchial blocker, the catheter showed no visible defect, but a bench test revealed a functional connection inside the catheter which allowed air to pass slowly from one bronchial cuff to the other. This technical defect relates to the unique design of the EZ‐blocker as it is the only bronchial blocker equipped with two bronchial cuffs. Clinicians should be aware of this inherent risk since complications may develop insidiously and affect both lungs simultaneously. Early recognition and prompt intervention can prevent life‐threatening intra‐operative deterioration.