Run the code, click on combobox (you have only 3 seconds on click), and observe the output.

What I see :

X : 860.0 Y 310.0
X1 : 860.0 Y1 511.0
Bounds in local BoundingBox [minX:0.0, minY:0.0, minZ:0.0, width:200.0, height:201.0, depth:0.0, maxX:200.0, maxY:201.0, maxZ:0.0]
Bounds in parent BoundingBox [minX:0.0, minY:0.0, minZ:0.0, width:200.0, height:201.0, depth:0.0, maxX:200.0, maxY:201.0, maxZ:0.0]

//About popup
X : 859.6000000238419 Y : 511.3999938964844
BoundingBox [minX:0.0, minY:0.0, minZ:0.0, width:216.0, height:46.0, depth:0.0, maxX:216.0, maxY:46.0, maxZ:0.0]
BoundingBox [minX:-8.0, minY:-8.0, minZ:0.0, width:216.0, height:46.0, depth:0.0, maxX:208.0, maxY:38.0, maxZ:0.0]
BoundingBox [minX:-8.0, minY:-8.0, minZ:0.0, width:216.0, height:46.0, depth:0.0, maxX:208.0, maxY:38.0, maxZ:0.0]
lv.localToScene(lv.getLayoutBounds()) BoundingBox [minX:8.0, minY:8.0, minZ:0.0, width:200.0, height:30.0, depth:0.0, maxX:208.0, maxY:38.0, maxZ:0.0]
X : 0.0 Y : 0.0
X : 859.6000000238419 Y : 511.3999938964844

Seeing lv.localToScene(lv.getLayoutBounds()) computations results, we can say, that listView is shifted on (8; 8) pixels (8 to right, 8 down). But at the same time, you can observe (move mouse on "1" in popup, and look at selection), that listView X and Y must the same, as popup X, Y (859,6; 511), which are the same, as left bottom corner of comboBox, which is located at 860, 511.

This makes us think, that listView is 8 pixels down and right, that it is actually is.

Please investigate, it is important for testing.