Previous button doesn't work for “youtube-ios-player-helper”

Question

I have a problem with "youtube-ios-player-helper" for iOS (XCode / ObjC), i.e. previous button doesn't work. Next song in playlist works, but previous song doesn't work. It works with custom buttons for next and previous, like in sample, but embedded controls for previous song in playlist doesn't work. Does someone have a solution for this problem?

Thanks in advance.