So one of my editors scheduled some posts for the night.
In the morning we couldn't find them in Twitter and Facebook, even though that WordPress published the posts.
Here is the last two lines from the log/history that might be related to the problem:
[2014-01-15 14:27:08] - [Skipped]- User ID 2 can't autopost - Post ID:(654)
[2014-01-15 14:27:08] - [*** ID: 654, Type: post]- Status Changed: future_to_publish. Autopost requested.