When you group the tree by a date field, the sort is made using the string resulting from the date to string conversion acording to the regional settings of windows.
Of couse, this create a crazy index if you don't use YYYY/MM/DD as your regional setting for dates, very rare for normal users.
To the user posting topics... PLEASE... I PRAY YOU!!! Don't put just 'ERROR' or 'Bug' in the topic.. I spend 30 mins checking all this post for seek any previous post of this problem.This is a big headache for every Tree or List control used. The controls developers spect that we show a string as 20040404 to the user? Why don't put a property to set this column as a date? (Sorry, programmer protest!
Sorry about my english, I speak spanish.