You can prevent this behavior by doing the following steps
1. Open the form in design mode
2. Go to “Form Option” in “Tool” menu bar
3. Select “Advanced Tab”
4. Select “Do Nothing(existing forms might not work properly)” value in “On Version Upgrade” dropdown list,
5. Click “Ok” and save the form
6. Publish the form to share point
I Hope this help you
Madhuri
InfoPath Dev
INDIA
Madhuri
http://www.ggktech.com