How to stop jQuery ajax from adding slashes to JSON string?

I am sending stringified JSON object to a wordpress action

console.log( JSON.stringify(alloptions) );

$.ajax({
    type: "post",
    dataType: "json",
    url: ajaxurl,
    processData: false,
    data: {
        'action': 'create_preset',
        'preset': JSON.stringify(alloptions)
    },
    success: function( response ) {

        console.log( response );

    }
});

the console log of the stringified object before sent via ajax is this

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so the string is correctly processed ,

but on the other side it comes out with slashes

function _create_preset(){

    if(!is_admin() && !isset($_POST['preset'])) return;

    print_r($_POST['preset']);

}

add_action("wp_ajax_create_preset", "_create_preset");

gives

{"get_presets":"eedewd","site_width":"1400px","layout_type":...

I know I can use

stripslashes( $_POST['preset'] )

to clean it up but that is what I am trying to avoid. I need the JSON string to be sent to the action as it is before the ajax, without slashes.

any help is appreciated!

and magic quotes is not on

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*UPDATE AND SOLUTION

Jesse nailed it and WP was causing the trouble.
Since the wp_unslash() is on its way to fix this in 5.0
https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards/issues/172
I added this to my code

global $wp_version;
$new_preset_options = $_POST['preset'];

if ( version_compare( $wp_version, '5.0', '<' ) ) {

    $new_preset_content = wp_unslash( $new_preset_options );

}else{

    $new_preset_content = $new_preset_options ;
}