Grouping with A formula issue

I am grouping on a date that was calculated using the following formula :

local stringvar d:= {TAGDTL.USER_DEF_TEXT_1}; //or database field

numbervar y:= tonumber ( '20' & d[5 to 6]);

numbervar m:= tonumber ( d[1 to 2] );

numbervar dd:= tonumber ( d[3to 4] );

date( y, m, dd)

The date displays fine, however when I group on it, it appears that it ignores the date completely.

The data in the detail shows up

10/14/2008

10/15/2008

10/16/2008 etc

however the group shows up with a completly different date.

Group = 10/12/2008

detail = 10/14/2008

detail = 10/15/2008 etc....

any ideas? Suggestions? help?

Thanks,

Jim