Multistep form returns to step 1 on page refresh with post data (TYPO3 9, form framework)

Question

I am designing a multistep form with the form framework which generally works fine. I am using a yaml form definition, the pages are defined like this:

renderables:
  - identifier: page-1
    label: 'Address'
    type: Page
    (...)
  - identifier: page-2
    label: 'Details'
    type: Page

However, when I am on page 2 or higher and I press the reload button in my browser, all my form session data is lost and I'm sent back to page 1.

I assume it is related to trusted properties, HMAC or C-Hash values, but I don't know where to start debugging. Can someone help me getting to the source of the problem?

Maybe it's a security feature in the form framework that every post request can only be sent once. As an advanced user, however, I would expect a website to allow refreshing a form.

The URL of the form has a chash parameter. These are the POST fields I got with Firefox dev tools:

tx_form_formframework[myform-1234][__state]
tx_form_formframework[myform-1234][__session]
tx_form_formframework[__trustedProperties]
tx_form_formframework[myform-1234][firstName]
tx_form_formframework[myform-1234][lastName]
tx_form_formframework[myform-1234][address]
tx_form_formframework[myform-1234][housenumber]
tx_form_formframework[myform-1234][zip]
tx_form_formframework[myform-1234][city]
tx_form_formframework[myform-1234][phone]
tx_form_formframework[myform-1234][email]
tx_form_formframework[myform-1234][emailrepeat]
tx_form_formframework[myform-1234][position]
tx_form_formframework[myform-1234][positionDifference]
tx_form_formframework[myform-1234][newPositionSelect]
tx_form_formframework[myform-1234][qCb6UuWPvJmAlgn3Tz]
tx_form_formframework[myform-1234][__currentPage]