acrobat pdf submit button for forms - fields order in xfdf

Question

My solution:

1. User opens PDF file on web server in browser.
2. User is entering form fields and pushing submit button.
3. Submit button sends XFDF data through POST to my PHP script.
4. When I get POST data, form fields are in random order.
5. I'm creating XFDF document based on POST and then process it further. Preferably fields should be in the same order as in PDF file.

Question:

I don't know how to control adobe reader to send form data in some predictable order. Form fields numbering (controlling flow of document when using TAB) is not changing resulting POST data order. Any ideas how to order fields?