You should be able to create ListSkin without having to use a scrollbar. Using a scrollbar shouldn’t be a requirement.

I just tried this example but couldn’t reproduce the error, perhaps I’m missing some files (like the itemRenderer that you’re using, I just used the default one) or specific steps to reproduce (I tried a small flex application with simple list with one item in Flash Builder). Do you see the error when you run the application, or when you switch to design view?

If you can reduce your application source to a small example that you can share, that’d be great. You can go ahead and report the problem at the forums here http://forums.adobe.com/community/labs/gumbo/ or log a bug here https://bugs.adobe.com/flex/

Thanks,
-Evtim