Alternated item color in list is not always alternated

In the WebEngine Cookie Browser example, the cookies are displayed in a list to the right, presented in alternated colors of white and gray which makes it easier to count the number of the cookies. Sometimes, this color is not alternated from one cookie to the next, displaying one cookie as white, and then the cookie directly under it as white instead of gray.

Steps to reproduce:

The simplest approach to reproduce this bug is to delete random cookies, reload the page, and see in the list if the behavior has occurred or not.

Expected behavior:

The cookies should always be displayed with alternated colors of white and gray. If one cookie is displayed with white, the cookie under it should be displayed with gray, and vice versa.