>> Why are you using the value queue instead of session queue?
The value queue contains all the parameters coming from the browser to the server. Since you are changing the value of one of these fields it makes sense to change the value in the Value queue as well. Then as it used later on (automatically) it is set to your "new" value, instead of the "original" value.
>> When is the complete form embed called?
when the user clicks on the Save button, before the record is written to disk.
cheers
Bruce