Layer.getData and correspondance between 'from' and 'to'

[ftoromanoff]

In the example source_fiole_geojson_raster.html, when we log the 'from' and 'to' parameter of the getData

    getData(from, to) {
        const key = this.source.requestToKey(this.source.isVectorSource ? to : from);
        if (this.id === 'pyrenees-orientales') {
            console.log(this.id, 'getData when source.isVectorSource');
            console.log('from', from);
            console.log('to', to);
        }
        let data = this.cache.getByArray(key);
        if (!data) {
            data = this.source.loadData(from, this)
                .then(feat => this.convert(feat, to), (err) => {
                    throw err;
                });
            this.cache.setByArray(data, key);
        }
        return data;
    }

we get this:

As we can see, sometimes we have exact correspondance between 'to' and 'from' and sometimes not.
I suspect that this should be homogene...