I have found the keep detail togther does not do much when you have items with in it that can grow. The detail section
seems to "keep together" as much as the original height of that section in the design.
SOme of this depends on if you have any items set to 'can grow'.
A few thoughts-
1 -You might consider creating another group level that allows the grouping for each detail record then set that goup to keep together in the group expert.
2 -You also might consider expanding the top of the sub report a bit to overlap the items you want to 'keep together'.
3 - push the fields into the sub report using shared variables
4 - consider using the overlay function
if none of these work please explain how you have items set up including the 'can grow' settings.