Prisoner release

Despite all the online coverage, I can’t seem to find a decent explanation of the prisoner-release “scandal”. I may well be wrong, but is the story that some foreign criminals, due to be released from prison anyway, weren’t considered for deportation? Nobody was released early, or without servicing a sentence, right? If so, is that it? Why’s it so important? What’s the difference between releasing foreigners and people who happened to be born in the UK, in practical terms? If the rules weren’t followed properly then, sure, there should be some kind of investigation, but given the uproar you’d think the country was about to slip into anarchy or something. Of course, I could be misunderstanding the whole thing…