confusing errors for structs with #[serde(flatten)]

[vthriller]

#![allow(dead_code, unused_variables)]
use std::collections::HashMap;

#[derive(Debug, serde::Deserialize)]
struct Config {
    foo: Option<String>,
    #[serde(flatten)]
    other: HashMap<String, usize>,
}

fn main() {
    let src = r#"
    aaa: 1
    bbb: true
    ccc: 3
    ddd: 4
    # and
    # a
    # lot
    # more
    # lines
    foo: bar
    "#;
    
    dbg!(deser_hjson::from_str::<HashMap<String, usize>>(src));
    dbg!(deser_hjson::from_str::<Config>(src));
}

The first message is what I expected to see for both calls to from_str():

[src/main.rs:25:2] deser_hjson::from_str::<HashMap<String, usize>>(src) = Err(
    Syntax {
        line: 3,
        col: 7,
        code: ExpectedU64,
        at: "true\n\tccc: 3\n\td",
    },
)

The second one always seem to point at the last line of the input:

[src/main.rs:26:2] deser_hjson::from_str::<Config>(src) = Err(
    Serde {
        line: 12,
        col: 2,
        message: "invalid type: boolean `true`, expected usize",
    },
)