It seems like setting "z" property to at least one item which is constantly visible on the screen breaks the algorithm which determines the areas that need to be redrawn. Try to run and play with the attached example (just scroll the list view a few times with different speed). You will notice that very often the bottom line of delegates still drawn somewhere below the tool bar (it's also noticeable on the attached screenshots). Using ListView is just the easiest way to reproduce this issue, but I've also observed that sometimes when I change visible property of an item covering the entire window and make it invisible, half of window becomes corrupted and contains leftover parts of the item I hid.