Qt Quick GridView changes scroll position when sorted

Question

I have a GridView (LtoR flow) that is sorted dynamically via a QSortFilterProxyModel. The GridView has 100 tiles at all times. I scroll down until visibleArea.yPosition is at e.g. 0.7 (70%). I wait for the model to update, causing the tiles to reorder. Since the nr of tiles doesn't change, I'd expect visibleArea.yPosition to stay at 0.7 - but it doesn't. It changes to other values (I can't really figure out a pattern). Likewise, originY changes automatically from 0 to higher numbers.

This means, for example, that if I scroll to the end of the grid and wait for a bit, I might actually be looking at the beginning of the grid after a while, due to these changes. I tried setting visibleArea.yPosition to the value it had at the end of the last user interaction whenever the data changes, but QML tells me that the property is read-only.

Why does the scroll position of the GridView jump around like this, and how can I stop it?

relevant QML code:

GridView {
    clip: true
    model: stateUiItemModel
    delegate: myDelegate
    anchors.top: commandArea.bottom
    anchors.left: parent.left
    anchors.right: parent.right
    anchors.bottom: bottomArea.top
    cellWidth: itemWidth
    cellHeight: itemHeight
    transformOrigin: Item.TopLeft
    cacheBuffer: 100

    visibleArea.onYPositionChanged: {
        console.log("ypos " + visibleArea.yPosition + " oy " + originY);
    }
}

output:

qml: ypos 0.7253333333333334 oy 0 // manually scrolled to this point
qml: dynamic sort enabled  // from here on GridView repaints with changed sorted order every 500ms
qml: ypos 0.6586666666666666 oy -200
qml: ypos 0.792 oy -400
qml: ypos 0.7253333333333334 oy -400
qml: ypos 0.6586666666666666 oy -500
qml: ypos 0.792 oy -700
qml: ypos 0.7253333333333334 oy -700
qml: ypos 0.6586666666666666 oy -600
qml: ypos 0.592 oy -500
qml: ypos 0.5253333333333333 oy -400
qml: ypos 0.45866666666666667 oy -300
// ... etc, new values every 500ms