NSTableView with overlapping corner views has odd scrolling

I'm trying to implement an NSTableView with rounded corners. The approach I took was to put a container on top of the table view that has images only on the corners to produce the rounded effect. The problem I'm having is that when the table scrolls, the corner images scroll with the row they were drawn on开发者_开发问答. Does anyone have insights as to why this is occurring?

Edit: I tried putting a button in the center of the corner image container and it seems like the NSScrollView is going on top when it's scrolling. When it scrolls, the button is also disappearing from the view. Is the scroll view known to do this?

Solved. I took the approach of creating a child window overlay. An example of this: http://lists.apple.com/archives/Cocoa-dev/2006/Apr/msg01638.html