ListView: Rendering glitch when section height changes dynamically

When a section height in a ListView changes dynamically, the new height isn't taken into account for rendering, and the section will overlap the items below it.

To reproduce, us the attached example. The section headers get enlarged if the mouse is hovered over one of the section's items. When a section gets enlarged, the section is painted over the first items of that section. Expectations: The items are pushed down and no painting overlap occurs.

Tested with:
qtbase: v5.0.0-299-g3d9a400
qtjsbackend: v5.0.0-2-gce0de18
qtdeclarative: v5.0.0-35-gd89f1db