When using QTabBar component, with many tabs, to make scrolling QToolButtons visible.
If we customize background color of these buttons with CSS like this :

QTabBar QToolButton

{ background-color:#ANYCOLOR; }

or
QTabBar QToolButton

{ background:#ANYCOLOR; }

..it will cause memory leak, each times the QTabBar is repaint. That's why we can create a timer to repaint often, and see the memory growth.
(For example, a blinking TabIcon, using setTabIcon will make the Tabs to repaint and cause the memory leak.)

We can bypass this leak by using an image instead of color in CSS :

QTabBar QToolButton

{ background:url(:/img/MY_BACKGROUND.png); }

..and the memory leak disappear.