user could use one Gift Coupon many times from the same browser - BUG

[FlorianGeorgiev]

Hi there, my setup is J! 3.4.5, VM 3.0.12., PHP 5.6.40, template with Virtuemart styling.
The shop works without registering. Users only fill in the Bill To and Shipment information.
I want to use a Gift Coupon. There's no problem to apply it but the problem is that the user can use it again and again for other products. This is not intended. In the backend it says that the Coupon is used, but the user can apply it again, when he/she is in the same browser. When I try another browser, the Coupon could not apply.
So the problem is that virtuemart somehow tells the browser to cache that info about the Coupon when it should be the opposite - virtuemart should tell the browser to invalidate that cache.
I'm not a developer so this might be wrong but there is definitely a bug.
Could anyone help me to make it work without updating?
p.s. Is it possible to restrict some file or link from caching in the .htaccess file so it invalidates the /cart page cache on every reload of the page?