Styles

I have created a report template in Word 2007 with a multitude of styles. The template is locked down so that formatting of text can only be done using the styles I have created.
Problem – Whenever text is pasted directly into the document, without using paste special-unformatted text, the text automatically pastes as my main heading style, even when I am in the middle of using a body text style. If I paste the text in the middle of a paragraph of body text style, then it appears as body text. Finish a paragraph, hit return and paste then it comes in as the main heading style. Does anyone have any thoughts why this is?