More specifically, the unwanted behavior happens when the height of the first delegate is reduced. I have attached a screenshot to better illustrate what's happening - this is after the delegate is resized, and you can see that the delegate is outside the view (because the text is supposed to be centered in the delegate). Also, if I scroll the list, the delegate will be fully visible once more.

This is the code that I've used to create this minimal reproducible example:

import QtQuick 2.11
import QtQuick.Window 2.11

Window {
    visible: true
    width: 640
    height: 480

    ListView {
        id: testList
        anchors.fill: parent
        model: 10
        verticalLayoutDirection: ListView.BottomToTop

        delegate: Rectangle {
            id: testDelegate
            width: parent.width
            height: 100
            color: index % 2 === 0 ? "yellow" : "green"

            Text {
                anchors.centerIn: parent
                text: index
            }
            MouseArea {
                anchors.fill: parent
                onClicked: {
                    testDelegate.height -= 20
                }
            }
        }
    }
}

The workaround I've used so far is to avoid using ListView.BottomToTop, and instead applying rotation: 180 to both the list and its delegates.

If necessary, I can also attach a zip file with the entire project, but it's just a newly-created empty QtQuick Application, with no changes made to it other the main.qml file, which I have shown above.