That "leaking" seemed to be related to another problem that I last saw
back on Classic (I haven't done many complex custom forms since we
switched to NWE): Sections are supposed to know what is under them. The
nice part is that if you moved a section header it would bring all the
contents of that section with it. Problem was, the editor often got
confused what fields and parts underneath were part of that section.
Sometimes it would smartly assume "everything until the next section,"
or sometime...