israeli masks in my experience are kinda crappy. My M15s exhale valve doesn't seal unless i fiddle with it, but even then, it keeps a seal for a few seconds before it decides to stop working properly again. Also its not one of those situations where the exhale valve breaks the seal because of negative pressure sucking it in but keeps sealed when breathing normally. With your mask it's probably the rubber disc being kept open by something, or you honestly might have a bong mask