Page reload when filling out a form in an iframe on iOS devices

I have a problem with iOS browsers

These are the conditions for the starter:
  - We have a simple html page that contains an iframe
  - the iframe also contains a simple html page with a form
  - the iframe has no scrolling and the dimensions are fixed.

Error:   Now if we open this page on iPhone (from Chrome / Safari browser) and start filling out the form, then at some point when text prints, the page scrolls by itself

This is an example link

<div id="container">

  <iframe src="https://www.w3schools.com/php/demo_form_validation_complete.php" frameborder="0"></iframe>

</div>

      

        
        
        
      

    

Why is this happening? How do you prevent these automatic page transitions?