Just to add my five pennyworth, in case it helps identify the problem. For no obvious reason, the date in Sims changes to US format, I have this happen maybe once a year. My computer / network was and is set to UK format. This morning I was working with Excel, IE, Sims and Outlook, they were all open. After downloading and importing a CTF file from S2S, it declared an error with overlapping school history dates, so I went to check the school history dates of the newbie, and the dates were all US format. I presumed they had come in on the file that way, and started to reverse them, but Sims was having none of it and all the dates in sims were now showing US format.
It would be worth noting if CTF import is responsible for anyone else's scenario, although it certainly doesn't happen every time we import a CTF.
Can I add that the dates in Sims were UK format, I had used some earlier in the day and the change happened while it was open.
Also, my remedy is to close Sims and reopen, it then reverts back to UK dates.