javascript related - Form is cleared when user presses back button

[eluser]Unknown[/eluser]
I am able to pass the variables back and forth
between windows(forms in the main and popup windows).
That is not the problem.
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Problem is
After the pop-up form comes up user enters the value and submits
inside the popup and the value is successfully populated in the main form.
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Now when the main form is submitted and verified sometimes there are some errors so, the users are instructed to go back and fix them. When user clicks the BACK button, all the entries in the main form are cleared.
THE ENTRIES ARE NOT CLEARED WHEN USER DOESNOT USE THE POPUP.

How do we avoid that?

Thanks