question for flashdata

[eluser]Shiro[/eluser]
I found out answer,
after use the flashdata
For example,
$this->session->set_flashdata('error', '<div class=\'message\'>Sorry, your username or password is incorrect!</div>');

It must be follow by refresh the page
redirect('welcome/admin','refresh');

if not the message would not display out, it need to run second time.

This is why, the set_flashdata('test','value') does work in the first place.

I think this is related with the machanism cookie, maybe the wiki of the flashdata need to state it out.