QAudioOutput (PulseAudio/Harmattan) playback stops after underflow

Trying to work around an issue with sound on Nokia N9. I am using QAudioOutput with a custom QIoDevice subclass. The code works flawlessly on Symbian phones, simulator and in Desktop builds.

On N9 however, my app reports buffer underflow; the following message is printed in debug output:

Got a buffer underflow!

Once the first buffer underflow occurs, audio stops altogether. Interestingly, data continues to be read from the QIoDevice. To restart any sound, new QAudioOutput instance must be created.