I was reading a posting of Ben Vollmer about "Doing Math in Microsoft CRM aka Calculated Field". This is an interesting article, but I noticed something in the posting that I did not know yet. There is a possibility to submit fields which are disabled! I have been using calculated fields before, but I always enabled the field when submitting the page.
So what is the solution? The use of the ForceSubmit attribute.
crmForm.all.field.ForceSubmit = true;
See the SDK for more info