If you are in the UK, how do you know which people you aren't allowed to publish stories about? How do you know if a super injunction is in force? Are they published somewhere?
We don't know that republishing the information is in contempt of court, but ignorance of the law is not (and never has been) a defense -- at best it's merely a mitigating factor for the court to consider when handing down a sentence.
It's clearly not, since republishing information (in this case, a statement from an MP using parliamentary privilege) is how we knew about Trafigura and other issues covered by a superinjunction.
The general public isn't informed (that's the point of a superinjunction) but how would they know about this anyway if they didn't know the subjects personally? Presumably there is some protocol for people who may be aware of what's censored, but suggesting that people can "accidentally fall foul of the law" is as realistic as suggesting a room of 7 billion monkeys randomly hitting typewriter keys will come up with Shakespeare.