Return_to tag on currency form not working

[kubrauzun]

We have a currency form with a return_to tag set to "back". See example:

{% form 'currency', return_to:  'back'  %}
{{ form | currency_selector }}
{% endform %}

This works sometimes, however, in some cases, it will take the customer to the following path instead /cart. I have tested with a relative path e.g., /collections/earrings, and same issue occurs. I can replicate the issue always in incognito and sometime in standard browser. 

Can someone explain what is causing the issue? Does the return_to tag not work in the currency form?

Thank you 🙂