It seems do_form_check() is checking each form's form_key value.

I am sure in each template file , I didn't modify the hidden field of each form.
Each form has its form_key , and with random generated value.

But I still don't know why it doesn't work ???

English is not my native language. I try my best to express my thought precisely. I hope you understand what I mean. If any misunderstanding results from culture gaps, I apologize first.