Thanks, Regis! Is there an admin setting to disable this feature? I’d like to not delete them automatically. If there is none (and I couldn’t find one) could you contemplate adding it?
When they are deleted, is any shadow of a trace left behind, for example in any messages they have been in? It’s really weird to me to see messages I have written to people who are no longer in the message. Now it looks like I am schizophrenic, talking to myself and giving myself all kinds of interesting names. 
Also, I think something went wrong in this case because these staged users I am talking about were created more recently, like in the last few weeks and months. None of them were created more than 1 year ago.