https://github.com/jenkinsci/jenkins/pull/6460 seems to introduce a regression for form validation for fields that are initially hidden under advanced section.

I've created a dummy plugin to make easier to see.

Having the plugin installed, going to Global configuration page, scrolling to the corresponding section and expanding the advanced section I'm observing this:

Form validation message is rendered for the field that's not under the advanced section, though no validation for the field under Advanced section.
doCheckAnotherField is invoked on page load and the corresponding response is received, but not rendered.