As of recently, a script has been reporting failures when trying to add a newly created youtube video to a playlist.
The flow is pretty simple:
URL bei
It seems indeed a bug, but, as far as I know, the site for post about bugs with the YouTube APIs is: Issue Tracker1.
The following link allows you create an entry on Issue Tracker.
It is worth check first if entries exists with the similar issue you're facing and if you find related entries there, please "star" that issue to draw attention to it and track updates, if you'd like.
1 Issue Tracker is shown (alongside Stack Overflow) at the end of the page of YouTube Data API website.