There are no scrollbars on DataRenderer or ItemRenderer. The ScrollBar's are either showing up on the List or a component within the item renderer. The List has a Scroller in its skin. You could try setting verticalScrollPolicy="off" on the scroller in the List skin or some of the components within your item renderer and see what's going on. Your first priority should be to identify which component has the scroller that's showing up.
I looked around and did not see scroller on anything but the list. I set both vertical and horizontal scroll policy to off. I still get the bars. I have attached a project I built to show what I am seeing.
ScrollBlink.zip 2.0 MB
Using min/max width and heights can have a momentary effect on scrollbar artifacts, i'm not sure if this is an application wide thing or more subtle, I know that the only times I see this 'strange' behaviour is when i'm using mx containers and size constraints, this is my thoughts on what is happening in some circumstances (could be wrong though) a vbox initialises to constraints thinks its viewport requires scrollbars enables them then the sizing or overrides decide scrollbars aren't needed and the correct behaviour is enforced. This is not just vboxes as I have seen this at the application container level which leads me to believe it has something to do with embedded size constraints. One note, I haven't seen this behaviour in the last couple of engineering pre-release builds so its either fixed or I have just subconciously changed the way I am coding (also I am refraining from using mx display objects unless there is no other option).