[REG 5.9.1->5.9.2] HiDPI: Horizontal/vertical lines visible when moving windows over Qt application

Since 5138fada0b9ce3968b23ec11df5f0d4e67544c43 HiDPI mode has rounding errors on expose events. When moving a window over a Qt applications window with HiDPI scaling, vertical and/or horizontal lines (borders from moved window) are visible (attached movies with scale 2.0 and 2.12). The bottom and/or right border of expose rectangle is not repainted due to rounding error.

Example - my idea what can be wrong:

We have a rect: x = 0.5, y = 0.5, w = 6.5, h = 5.0
Now we round it (floor/ceil): x = 0, y = 0, w = 7, h = 5 (bottom line is not repainted)
But we expect: x = 0, y = 0, w = 7, h = 6