I am thinking the stylename for the Table of Contents heading is probably not changing. But it is possible the style definition is changing because you have set the styles to refresh on opening. This could make that entry appear in the TOC without changing its style.

Can you verify the stylename for the TOC heading is the same in both documents?

Can you check that Developer > Document Template > Automatically update document styles is UNCHECKED in both documents?

And then show us the field code used by the TOC by selecting the TOC and pressing Shift-F9

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Andrew Lockton
Chrysalis Design, Melbourne Australia