Using php curl to fill form on asp.net page - php

Question

There is a asp.net driven site where I can login and fill a form to place a order after a succesful login. This needs to be done by my server with curl.
Whenever I do this with my browser there is nothing special.
I go to example.com/login.aspx. Fill in fields and post it back. I get a index page back for logged in users. After this i need to click on a link to the form for order placement. Doing this gives me the form, which I fill and send back.This yields the wanted result of an placed order. Analysing the source revealed the page gets submitted through javascript,but the server cannot know how the request is sent if the request is identical. During this process i kept track of all the post requests send from my browser.
Having all the post requests, i wrote some code to do the same with curl.
The algorithm is:
Send a get request to obtain the example.com/login.aspx page
Parse the responds for any hidden fields(as they are used to mimic a statefull connection)
Post the state and the logindata to example.com/login.aspx
Parse the state send back and update it
Get form for order placement
Parse & update the state again
Post the state and the same post data that my browser sent
Print info to file instead of STDERR
During the process cookies are used with curl.
Everything goes smooth until the last POST. Instead of a "Success" or "Failure" result, I get my original form returned to me, with no validation errors mentioned. If I delibarely fill in gibberish or leave some things empty with my browser I get validation errors shown.
I have no experience with asp.net and am completely stuck here, so forgive me if this question is too specific.
Question:
If the headers and post data are exactly the same as from my browser, how can my curl operation have a different result?
For completeness:
POST from browser:
POST /DataEntry.aspx HTTP/1.1
Host: www.iftin.co
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20100101 Firefox/16.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
Accept-Language: nl,en-us;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
Referer: https://www.iftin.co/DataEntry.aspx
Cookie: ASP.NET_SessionId=SomethingX; .hawAuth=SomethingY
Content-Type: application/x-www-form-urlencoded
Content-Length: 10111
Post send by Curl:
POST /DataEntry.aspx HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20100101 Firefox/16.0
Host: www.iftin.co
Referer: https://www.iftin.co/DataEntry.aspx
Cookie:.hawAuth=SomethingZ; ASP.NET_SessionId=SomethingW
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
Accept-Language: nl,en-us;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Length: 25236
Expect: 100-continue
Content-Type: application/x-www-form-urlencoded;boundary=----------------------------5bb8ec4e5ecc
If people want to see some code, let me know. Thanks for reading and spending time on this.
Ater writing this, I noticed that the Content-Length for my curl request is substantially bigger than for my browsers request. I copied all parameters in the body of the Post of the browser to my code and passed it to curl in a array.
So curl has to add some data to the request by default. Is this the case?
The CURLOPT_SSL_VERIFYPEER is set to false, while the page uses SSL. Could this be it? Why?