QTextToSpeech m_utteranceCounter does not actually represent index in queue

The description of enqueue says

"Adds \a utterance to the queue of texts to be spoken, and starts speaking.
 Returns the index of the text in the queue, or -1 in case of an error."

But m_utteranceCounter is never actually decremented and only zeroed in Stop(). So if you never call stop but keep queueing, then this value grows indefinitely. So this doesn't actually represent the index correctly, as it isn't decremented when dequeueing. I would think you should either decrement m_utteranceCounter where m_pendingUtterances is dequeued in updateState, or just return the size of the queue -1 as that is where the enqueue string will be.