It sounds like you've placed your summary field in a Sub-Summary part. The part will only be visible if you sort the found set by the part's designated sort field and this would explain what you describe.
place the field in a trailing grand summary part, a header or a footer and you should see the same "sum of the entire found set" regardless of sort order.
That gives me a grand total across all dates but does not give me a total for each date. Perhaps some sample data would help me explain what I want:
I want the summary field to show 7 (i.e., 3 + 4) any time I'm in Form view on a record that has a date of 8/3, and 12 (i.e., 9 + 3) any time I'm in form view on a record that has a date of 8/4.
Then you have to sort your records by date. The records must be grouped in clusters of records of all the same date or your summary sub-totals will be meaningless.
What problem are you trying to solve by not having the records sorted by date?
Ya said the magic word..."Form View"...so it isn't a subsummary report.
One way to do this would be:
Self-join to another TO (Self2) by the date value
Have an unstored calculation field (not summary field) in your table that equals Sum(Self2::Value)
It works in my brain, and I'm pretty sure I've used it before succesfully...but the brain is foggy today...
Does this work for you?
Edit: doing it this way might be sort of confusing for other users of the Dbase who don't understand where the summation comes from...think about how others would percieve the number and possibly consider a portal so that they know where the number comes from...