set Dynamic Default values for CHECKBOX in different pages

I tried setting the shortcode attribute with the value, like this:

Page 1
[contact-form-7 id=”7″ title=”Contact form 1″ checkbox-246=”Option 1″]
page 2
[contact-form-7 id=”7″ title=”Contact form 1″ checkbox-246=”Option 2″]

In the page 1 is showing as default “option 2″, looks like is taking the last form I saved.
If I’m going back in the page one (in the backend) the shortcode is changed with checkbox-246=”Option 2″ and if I change with checkbox-246=”Option 1″, it will change in the page 2 with checkbox-246=”Option 1” as well.