Wrong encoding of text keys

[moxian]

Problem: png's encoded by lodepng seem to lack text_keys, as seen by the png crate and a certain non-rust closed-source application that i care about.
Given png's very strongly worded claims of standard compliance (and that png-produced images are recognized by the aforementioned non-rust application, whereas the lodepng ones are not), i assume the fault lies with lodepng.
Sadly i have not delved deep enough into the standard to provide any more specifics.

Code demonstrating the issue:

extern crate lodepng;
extern crate png;

fn main() {
    let image = vec![255u8, 0, 0, 255]; // single red pixel
    let mut encoder = lodepng::Encoder::new();
    encoder.info_png_mut().add_text("hello", "world").unwrap();
    let encoded_image = encoder.encode(&image, 1, 1).unwrap();

    // parse it back
    {
        println!("\n -- lodepng view of the metadata:");
        let mut decoder = lodepng::Decoder::new();
        let decoded = decoder.decode(&encoded_image).unwrap();
        // displays keys properly
        println!("the following text keys are present:");
        for (k, v) in decoder.info_png().text_keys() {
            println!(
                "{:?} - {:?}",
                std::str::from_utf8(k),
                std::str::from_utf8(v),
            )
        }
    }

    {
        println!("\n -- png view of the metadata:");
        let decoder = png::Decoder::new(encoded_image.as_slice());
        let mut r = decoder.read_info().unwrap();
        println!("{:?}", r.info());
        // displays nothing
        println!(
            " compressed text: {:?}\n uncompressed text: {:?}",
            r.info().compressed_latin1_text,
            r.info().uncompressed_latin1_text
        );
    }
}

Output:

 -- lodepng view of the metadata:
the following text keys are present:
Ok("hello") - Ok("world")

 -- png view of the metadata:
Info { width: 1, height: 1, bit_depth: Eight, color_type: Rgb, interlaced: false, trns: None, pixel_dims: None, palette: None, gama_chunk: None, chrm_chunk: None, frame_control: None, animation_control: None, compression: Fast, source_gamma: None, source_chromaticities: None, srgb: None, icc_profile: None, uncompressed_latin1_text: [], compressed_latin1_text: [], utf8_text: [] }
 compressed text: []
 uncompressed text: []

[kornelski]

Have you checked the utf8_text field?

[moxian]

Yes, i have. It's empty as well (again, as per png crate; i have not inspected the encoded bytes).
Playing with encoder.set_text_compression() does not change things either.