? submitting form values changed by JS

Hallo
i have one page with 2 forms A and B, each one already filled at the beginning.
Then i fill B with values automatically taken from A, and submit the B: but the values that i find into POST[] are the original ones of B, not the new ones.
Actually, when B is filled from A, i can see A values into textareas of B in the browser window, but if i take a look at the HTML source i find the original values, the same that are POSTed.

I use a plain HTML submit button to submit the form.
What am i missing?

TIA

Could be a timing issue. If you aren't requesting a return value from the function that changes the values, then it's possible the form submits before the function changes the data. How are you calling the function?

the "B-filler function" is called manually, and so the submit, that is possible only after the filling has been completed.
The filler simply uses the syntax

forms[1].field.value=forms[0].field.value;