Lushh - the automatic saving of a bound record on a form seems to be a 'feature' of Access that can not be disabled, per se.
The way I've gotten around this when necessary (and it's ugly, to say the least) is to use a temporary table to hold the data on your 'working' form, and when the "Save" button is pressed, I call a quick SQL INSERT INTO.. query to shoot the temporary record into the table that I want it in, and then delete the temporary record.
If the form is closed without the "Save", you've only saved into the temporary table, and that can easily be scratched when you're finished.