Another one of the Flex gotchas…I spent way too much time on this only to have an adobe engineer himself answer this on the flexcoders mailing list:
I had created custom renderers for my list and it looked great. But there was a 2 pixel gap between the renderers that was driving me insane. After my own efforts went nowhere I asked the question on the flexcoders mailing list. The answer, use paddingTop and paddingBottom = 0 in your style. The Flex documentation on the 2 styles says “Number of pixels between the container’s {…} border and the {…} edge of its content area”. This is definitely not something I would read and use that property to manage my item renderers in a list. Ah well, now I know better :).
This tip is going straight to flextips.corank.com, a site dedicated to these weird gotchas and helpful hints. Do check it out and post your own tips there.