Si Captcha and Guestbook Issue

Hi,
I have the last wordpress and plug in version.

My guestbook is here:
http://www.marcoborla.it/guestbook-mb/

If the captcha is not compiled all data digited in the form are lost when you press back button.
Is possibile to keep the text?

How reproduce:
Compile the form but not put any captcha.
Send and you will see error message on a new page.

If you press back button all previous text are loosed.

https://wordpress.org/plugins/comment-guestbook/