Bug introduced in commit 0d9111a5: iniSet* functions would write key/values to the end of the list when the root section (NULL) was specified, rather than the beginning of the list.
The root section always starts at the beginning of the list/file, so I'm not sure why section_start() was doing anything other than returning 0 for the root section. It's possible this now breaks iniSortSections() in some way, so that should be retested with a file with a root section and named sections.