soundio_outstream_pause doesn't always work as expected

I'm running the `sio_sine` test and I've noticed that sometimes happen that when I select to pause the audio (pressing `p`) the audio is not paused even if the call to `soundio_outstream_pause` seems to return `no error`.
I've noticed that this happens more frequently if I'm running an audio player in the background (e.g.: Clementine or Amarok).

Backend: PulseAudio
Output device: Integrated audio device Realtek ALC1150 (motherboard: Gigabyte Z170X Gaming 5)
Software latency: 2.0
OS: Arch Linux 4.4.5-1 (64bit)
Desktop environment: Deepin