Huge output gaps in duplex mode

[bluenote10]

When using duplex mode, I'm getting serious gaps in the audio output. This is in release mode, and even if I increase the frames per buffer to buffers sizes corresponding to multiple seconds, there are gaps between the buffers. The gaps are approximate 1 sec long. A minimal example to reproduce looks like this:

use std::io;
use portaudio as pa;

const CHANNELS: i32 = 2;
const SAMPLE_RATE: f64 = 44_100.0;
const FRAMES_PER_BUFFER: u32 = 1024;

fn main() {
    run().unwrap()
}

fn run() -> Result<(), pa::Error> {
    let pa = pa::PortAudio::new()?;

    let mut settings = pa.default_duplex_stream_settings(
        CHANNELS,
        CHANNELS,
        SAMPLE_RATE,
        FRAMES_PER_BUFFER,
    )?;
    settings.flags = pa::stream_flags::CLIP_OFF;

    let callback = move |pa::DuplexStreamCallbackArgs { in_buffer, out_buffer, frames, time, .. }: pa::DuplexStreamCallbackArgs<f32, f32>| {
        for i in 0 .. out_buffer.len() {
            out_buffer[i] = ((i * 2 % 1000) - 500) as f32 / 1000.0;
        }
        pa::Continue
    };

    // Start stream
    let mut stream = pa.open_non_blocking_stream(settings, callback)?;
    stream.start()?;

    // Wait for user input to quit
    println!("Press enter/return to quit...");
    let mut user_input = String::new();
    io::stdin().read_line(&mut user_input).ok();

    stream.stop()?;
    stream.close()?;

    Ok(())
}

I can run the same example in other languages just fine, which indicates it is a problem in the Rust binding themselves.

The non-duplex variant using default_output_stream_settings also runs fine.