Dragging icon to newly created launcher page makes it disappear

This was seen with qt-qml HEAD at 337dbd5391b4e2b1bd88918a46f3392df8fd1312
and tesla HEAD at fc973ce8ddc01f9834727b22fc1dbebd66e6df60

Open the launcher and scroll to the last page. Long-press an icon and drag it to the new
empty page on the right. Note how the icon disappears on releasing the mouse button.
Tap the spot where the icon should be, and note that there indeed is an item there, but
it has no icon and no text.

See code for handling the drop in GridPage.qml lines 133-142. Note how debug output
seem to indicate nothing is wrong. See AppList.qml for the code that adds and removed
launcher pages.