Description:
When a user is filling out a form (in my case, the Solspace User registration form), has an error in their input, is taken to the Custom System Messages Submission Error template, and then hits the back button to return to the form their data is lost / the form fields are all empty.

At first I thought this was a front-end issue, but the only way I’ve been able to reliably make the issue go away is by disabling the Custom System Messages extension and retesting with EE’s standard error message template.

While attempting to debug / work around the issue I’ve tried redirecting to a default Submission Error template (/error/index) and also tried using a Custom Action to redirect back to the same template where the form data is being lost. When using a default template the form data is saved in Chrome and Safari, but is not saved in Firefox or IE. When redirecting back to the same template the form data is not saved in any browser. 

The form I’m having trouble with can be found here:
https://skylinefurnituremfg.com/trade/request-access

I created a quick reduced test case that contains nothing but the Solspace User registration form tags and am seeing the same behavior:
https://skylinefurnituremfg.com/trade/test

The error template doesn’t include anything custom / unique. Here’s the code (minus all the header, footer, and wrapping markup):
{if csm:content}

{csm:heading}

    {csm:content}

« {csm:link}

{if:else}
    {redirect="/"}
{/if}

Detailed steps to reproduce the issue:
1. Go to url above and fill in form. Enter mis-matched passwords to trigger error (the other required fields are caught with front-end validation).
2. Browser is redirected to custom error template.
3. Hit back button to return to form.

I’ve included a login to the staging site below. It’s a mirror copy of the production site, but the client doesn’t have an SSL certificate for it, so I figured it was better to include links to the actual production site when referencing the issue itself. But if you want to login to double-check any config details have at it.

Thanks in advance for taking a look and don’t hesitate to shout if there’s any more info I can pass along that would be helpful.