react-native: border top/left/bottom/right width not working

I have this in my render method:

    return View(
      { style: { flex: 1 } },
      TouchableWithoutFeedback(
        { onPress: this.handlePress },
        View({
          style: {
            flex: 0,
            backgroundColor: 'gray',
            height: 50,
            alignItems: 'center',
            justifyContent: 'center',
            borderWidth: 1,
            borderColor: 'white'
          },
        }, Text({ style: { color: 'white' }}, "^"))
      ),
      TouchableWithoutFeedback(
        { onPress: this.handlePress },
        View({
          style: {
            flex: 0,
            backgroundColor: 'gray',
            height: 50,
            alignItems: 'center',
            justifyContent: 'center'
          },
        }, Text({ style: { color: 'white' }}, "v"))
      )
    )

It renders this:

But if I change the borderWidth in the first component to borderBottomWidth or any of the other top/left/bottom/right methods, there is no border. There should be a white border on one side of the component: