[SectionList][inverted] SectionList headers are sticky-at-the-top-footers if the list is inverted

• I have reviewed the documentation
• I have searched existing issues
• I am using the latest React Native version

Environment

Environment:
OS: macOS High Sierra 10.13.1
Node: 8.6.0
Yarn: 1.5.1
npm: 4.6.1
Watchman: 4.9.0
Xcode: Xcode 9.0.1 Build version 9A1004
Android Studio: Not Found

Packages: (wanted => installed)
react: 16.3.1 => 16.3.1
react-native: 0.55.3 => 0.55.3

Steps to Reproduce

Clone this repository and run it via react-native run-ios.
Observe the section separators are in wrong (randomly?) places.

Expected Behavior

The section list headers should be in the top of the section instead of the bottom like section footers do with an inverted list (but they aren't sticky).

Expected gif:

Actual Behavior

The section headers are footers instead of headers. They are sticky because of https://github.com/facebook/react-native/pull/17762 but still footers, not headers.

Sample code:

export default class App extends React.Component {
  render() {
    return (
      <View style={s.container}>
        <SectionList
          inverted
          sections={mock.sections}
          maxToRenderPerBatch={10}
          initialNumToRender={10}
          style={{ flex: 1 }}
          keyExtractor={(item) => item.messageId}
          renderSectionHeader={sectionProps => (
            <SectionHeader
              {...sectionProps}
            />
          )}
          renderItem={({ item }) => (
            <ListItem
              item={item}
            />
          )}
          ItemSeparatorComponent={ItemSeparator}
        />
        />
      </View>
    );
  }
}

Problem Gif:

Commencez par cloner la reproduction React Native liée et l’exécuter avec react-native run-ios afin d’observer le comportement inversé de SectionList. Examinez le point d’entrée de SectionList et la gestion existante des listes inversées, puis comparez le résultat avec les GIFs attendu et du problème ; c’est terminé lorsque les headers restent en haut de leurs sections au lieu de se comporter comme des footers.