Does CodeIgniter convert all post variables to get variables?

I don't think CI would move POST vars to GET. Maybe snippet of code you are using would help troubleshoot it.

Here is some of the code:

javascript code in page:

string1 = '<input type="hidden" name="searchDateStart" value=' + dblquote + searchBegin + dblquote + ' />';
$('#frmMain').append(string1);
 document.forms[0].action = link;
 document.forms[0].submit();  
 
 web address after the form is submitted:
 
//xxx.com/xxx/xxx/date?searchDateStart=2016-02-24&searchDateEnd=2016-02-29

note; had to remove the http to prevent the forum from changing the above to a link

and here is some code from the model:
     $allPost = $this->input->post();
     $allGet = $this->input->get();

$allPost was 0, $allGet was 2