BUG: Get free shipping by enabling and disabling JS :S

[oliiix]

Dear Prestashop Developers

We just had an incoming order with a product for 8.- via carrier "swiss post priority". This should have added 9.- shipping costs to the 8.-.
After few minutes I found out how this might have gone:

With JS enabled:
- go to checkout page
- fill out the form (adress details if as guest)
- select a carrier without shipping costs
- DISABLE JS
- now I had to load the page again (not sure if a reload would work), not quite sure why
- select the carrier with the shipping costs
- ENABLE JS
- check the terms&conditions checkbox and click on the payment method you want.
- somehow the price isn't being updated with the shipping costs even when moving on and finishing the order process completely. also in the admin backend, the shipping costs are not visible.

P.S. Prestashop Version: 1.6.1.17

Edited November 14, 2017 by oliiix (see edit history)