Since MagentoCE2.1.11, after swithing store view, ___store=xx is added to url. Breaks 'back' functionality.

[bobemoe]

Preconditions

PHP 7.0.27-1-dotdeb+8.1 (cli) ( NTS )
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
with Zend OPcache v7.0.27-1-dotdeb+8.1, Copyright (c) 1999-2017, by Zend Technologies

nginx version: nginx/1.12.2

Linux 3.16.0-5-amd64 #1 SMP Debian 3.16.51-3+deb8u1 (2018-01-08) x86_64 GNU/Linux

mysql Ver 15.1 Distrib 10.0.32-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2

Steps to reproduce

1. Clean install of magento2.1.12 using composer.
2. Admin->Stores->Add Store View (name: test, code: test, enabled)
3. Fontend use store switcher to change store view to 'test' store. Notice that ?___store=test is added to the URL.
4. Navigate to another page (e.g. terms)
5. Click 'Back' in the browser

Expected result

The previous page is displayed

Actual result

Firefox complains "Expired Document"

Notes

I've tested this with the different version of magento. It seems that before 2.1.11 the ?___store= was not added to the URL and switching was handled, i guess, purely by POST/session/cookie.
Since 2.1.11 the ?___store= is added upon switching and going back to any page that has that in the URL causes this issue.

[magento-engcom-team]

@bobemoe , thank you for your report.
We've acknowledged the issue and added to our backlog.