Change date format on Group & Sort

Member for

16 years 3 months

I am using version 6.2  and when I group by start and interval by day I get DAY M YY

my user prefernce is set to Day, Month, Year 

and Month Name and Leading zeros are both checked

Member for

20 years 6 months

I've tried the same and I also get month-day as the format when grouping by day. I think this is just the default use for Grouping by Dates.