strange behaviour of input->post()

[eluser]Soruman[/eluser]
Dear Codeigniter Community,

Today I've encountered something strange about input->post().

I am posting data using ajax to a Codeigniter page,

Using print_r ($_POST) returns data;
Even using print $this->input->post('KEY') returns data,
but $this->input->post() returns FALSE, like the post array is empty.

I was trying to use validation but couldn't be sucessfull. After struggling with the code a while, I tried this for debug and noticed this problem.

What can be the reason for it?

Thanks in advance,