Smart playlists are empty on iPad after iOS 4.2

My iPad had just got the issue. My smart playlists were empty after updated to iOS 4.2.Here is a work around. Just put those smart playlists in one or more folders and they will show up on your iPad. The steps is the following:On your PC, click File > New Playlist folder in the iTunes, and drag your smart playlist into the folder. Then drag the folder onto the iPad in iTunes. After done