The use of <f:section> elements inside newly-added items in a hetero list are broken. This appears to be caused by the introduction of resource adjuncts in Jenkins 1.455.
The generated html of a <f:section> entry changed in v1.455 to include these extra elements:
<link rel="stylesheet" href="/adjuncts/29830985/lib/form/section_.css" type="text/css">
I believe it is the link element causing the problems because if I wrap the <f:section> in an <f:advanced> tag, then edit the DOM to remove the <link ... href="/adjuncts/29830985/lib/form/section_.css"> element, then the hetero list entry loads successfully when the advanced section is expanded.
An example of this is the Sectioned View Plugin. If you add a new List View Section to a Sectioned View then the Advanced section (which contains a <f:section> tag) is empty when expanded in Jenkins 1.455+. If you edit the DOM immediately after adding the List View Section (before clicking the Advanced button) to remove that extra <link ...> element, then the Advanced section will work properly.