[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:

まず、リンク先の React Native の再現コードを clone し、react-native run-ios で実行して、反転した SectionList の動作を確認します。SectionList のエントリポイントと既存の反転リスト処理を調べ、その結果を期待される GIF と問題の GIF と比較します。完了の条件は、header が footer のように動作するのではなく、それぞれのセクションの上部に留まることです。