Here's my preferences.
And today it says my last logged in date is 3 September 2015, just as I expected as it's seeing my local date as 9/3/2015.
What is happening is that Thwack is taking by local date of 9/3/2015 (DD/MM/YYYY) and Americanising it to be 3rd of September 2015 (MM/DD/YYYY). So the Last Logged In date is set to the Locale of United States. It should be set to be at what ever is in my preferences.
But I'd really like to see what happens when my local date is 13/3/15 as there is no 13th month