Trying to modify currency display – Some javascript probably messes it up

Hello.

I am developing a plugin that changes the currency display.

But the problem is that the new displayed value is there only for around ~0.5 seconds.

When i change the currency with url /?hh_currency=USD
and /?hh_currency=EUR
the displayed currency in the top navigation bar cart is only shown for ~0.5 seconds.

If i add a product to the cart, it displays it ok after that.

So how can i fix this?

a screenshot of the error
https://www.dropbox.com/s/x9mopdjsvtmbfnp/CurrencySwitching_not_working.png?dl=0

screenshot 1 is shown when you come to the site
screenshot 2 when you change the currency (url above)
screenshot 3 is shown around ~0.5 seconds after changing the currency.
should not go to the stage 3.

i think some javascript reverts it back to the old value when changing the currency????

WordPress 5.0.2
Theme: StoreFront
Installed plugins (2): WooComemrce, this test plugin.

Here’s a TEST code to demonstrate the problem.

<?php
/**
 * @package heikin_test_currency
 * @version 0.1
 */
/*
Plugin Name: Heikin TESTIT - Currency
Description: Testing some currency things
Author: Me
Version: 0.1
*/

if (!defined('ABSPATH'))
	exit;

class hh_dual_currency_rates_test
{
	public function __construct()
	{
		add_action( 'init', array($this, 'process_get_post' ));

		add_filter( 'woocommerce_get_price_html', array($this, 'custom_price_message' ));
		add_filter( 'woocommerce_cart_item_price', array($this, 'custom_price_message' ));
		add_filter( 'woocommerce_cart_item_subtotal', array($this, 'custom_price_message' ));
		add_filter( 'woocommerce_cart_subtotal', array($this, 'custom_price_message' ));
		add_filter( 'woocommerce_cart_total', array($this, 'custom_price_message' ));
	}

	function custom_price_message($price)
	{
		if ($_SESSION['hh_currency'] == "USD")
			return '<span class="woocommerce-Price-amount amount">$12.34 USD-test</span>';
		else
			return $price;
	}

	function process_get_post()
	{
		if( !session_id() )
			session_start();

		if( isset( $_GET['hh_currency'] ) )
		{
			$_SESSION['hh_currency'] = preg_replace("/[^A-Z]/", "", $_GET['hh_currency']);
			
		}
	}
}

global $hh_rates;
$hh_rates = new hh_dual_currency_rates_test();