generating of capture and data submitting

Hi,
In 3.1.0, ENVIRONMENT=development project I made a form for user registering which is added by form submitting

Code:

<form role="form" class="form-horizontal" action="[url=http://local-wprods.com/register]http://local-wprods.com/register[/url]" method="post" accept-charset="utf-8" id="form_register" name="form_register" enctype="multipart/form-data">
<input type="hidden" name="csrf_test_name" value="6d03687881325a26166f0d4eac973383" />
...

I use ajax code for (re)generating of capture and when setting values for capture
I see next parameters

Code:

$this->session->userdata('register_expired_time')::Array
(
[__ci_last_regenerate] => 1482328063
[register_word] => gczzmr
[register_expired_time] => 1482335263
)

But submitting form I see:

Code:

$this->session->userdata('register_expired_time')::Array
(
[__ci_last_regenerate] => 1482328380
)

session is different and generated word/time are empty.
Why so and how to fix it? Can both generating of capture and data submitting be made in ajax?
Which decision is better ?
Thanks!