Gateway throws java.lang.IllegalStateException requiring restart

Issue

Under load, randomly, one of the gateways stops accepting further requests. The problem is first noticed in an exception handler, although the actual exception is never reported. The exception handler tries to call release() on the gateway's ShutdownHandler, but this call fails with the following exception and we are forced to restart the gateway:

2015-12-01 23:10:54,165 | ERROR | entloop-thread-2 | DefaultContext                   | 266 - io.fabric8.fabric-vertx - 1.2.0.redhat-133 | Unhandled exception java.lang.IllegalStateException: Unbalanced calls to release detected.
    at io.fabric8.common.util.ShutdownTracker.release(ShutdownTracker.java:78)[65:io.fabric8.common-util:1.2.0.redhat-133]
    at io.fabric8.gateway.handlers.detecting.DetectingGateway.handleShutdown(DetectingGateway.java:430)[268:io.fabric8.gateway-core:1.2.0.redhat-133]
    at io.fabric8.gateway.handlers.detecting.DetectingGateway.access$400(DetectingGateway.java:54)[268:io.fabric8.gateway-core:1.2.0.redhat-133]
    at io.fabric8.gateway.handlers.detecting.DetectingGateway$6$2.handle(DetectingGateway.java:410)[268:io.fabric8.gateway-core:1.2.0.redhat-133]
    at io.fabric8.gateway.handlers.detecting.DetectingGateway$6$2.handle(DetectingGateway.java:407)[268:io.fabric8.gateway-core:1.2.0.redhat-133]
    at org.vertx.java.core.net.impl.ConnectionBase.handleException(ConnectionBase.java:126)[266:io.fabric8.fabric-vertx:1.2.0.redhat-133]
    at org.vertx.java.core.net.impl.VertxHandler$2.run(VertxHandler.java:104)[266:io.fabric8.fabric-vertx:1.2.0.redhat-133]
    at org.vertx.java.core.impl.DefaultContext$3.run(DefaultContext.java:175)[266:io.fabric8.fabric-vertx:1.2.0.redhat-133]
    at org.vertx.java.core.impl.DefaultContext.execute(DefaultContext.java:135)[266:io.fabric8.fabric-vertx:1.2.0.redhat-133]
    at org.vertx.java.core.net.impl.VertxHandler.exceptionCaught(VertxHandler.java:96)[266:io.fabric8.fabric-vertx:1.2.0.redhat-133]