Crash when calling QBluetoothDeviceDiscoveryAgent's start() method with Bluetooth powered off

I created a "hello world" application to test Bluetooth device discovery using QBluetoothDeviceDiscoveryAgent.

However, if I call the 'start()' method of that class with Bluetooth powered off, my app crashes and goes away. The debug console prints this:

[Qt Message] void QtMobility::BluetoothLinkManagerDeviceDiscoverer::setError(int) errorCode= -44
Thread has crashed: Thread 0x49c has panicked. Category: KERN-EXEC; Reason: 0
Thread has crashed: Thread 0x49d has panicked. Category: KERN-EXEC; Reason: 0

The problem does not occur if I turn on Bluetooth before, either manually or programatically (e.g. using QBluetoothLocalDevice and its method 'powerOn').