Coupon Code remains in the field

Hi
I added a step after the cart and the login for the coupon code.
Now I put in a coupon code, but after logout the coupon code remains in the coupon field.
Even if I open a other browser (from FF to Google e.g.), the coupon field is already filled out with a coupon code.

Hi,

I've never seen that.

Can you give a link to your shop so that we can see that ?

Maybe it's a caching issue ? Can you check that all caching is deactivated on your website ?
Disable the cache in Joomla configuration.
Site -> global configuration -> system -> "Cache settings".
Disable, if it's enabled, the joomla cache plugin.
Check your template' options for a potential cache option and deactivate it.