This is most likely happening because of one of two reasons:
- page template inheritance is set incorrectly
- there are orphaned webpart contents in the document. Go to the page and click on the General tab of the properties and scroll to the bottom. Click the Edit regions and webparts button in the Advanced section. Check the names/id's of the items there and compare them to your webparts IDs on the page template. If you find duplicate data, just remove one of them.