If Word is opened, it normally opens with a blank document. If you click on a Recent File, it does this? You state it does not do it if Word is open with another document. Does it do it under the above circumstance. technically there is another document, but it is not really a document yet, as it is not saved.
In any case, this is odd. There was another thread regarding style title text being inserted into a blank document. However, in that case ALL the basic styles were inserted as text.
1. have you removed all base styles, with just Heading 1 left?
2. have you recently had a recovered file? Something caused an error, and Word did a recovery?
3. have you any macros in normal.dot, or any global template that creates new files?
Gerry