OS: Debian 9 Browser: Firefox (latest) on Windows 10
Behavior: When error is caught on form submit, clicking on back button on error page goes to the wrong page (1-2 pages ago) instead of the form the erroneous value was entered on.
Steps to reproduce: System Settings > Server Templates > Default Settings > Apache Web Site > URL for webmail domain > enter invalid value and submit form. Press the button to go back and correct the error.
This happens throughout virtualmin and causes loss of form contents on error.