I created a Custom paragraph style for a chapter break symbol. The symbol is a single asterisk, the Style centered with space above and below. If I AutoCorrect my document, the custom Style is changed to Default and the asterisk left aligned. I actually have no Default Styles in the document, and this happens even if everything in the Autocorrect Options is unchecked.
I believe that sometimes when the autocorrect does it’s thing, it also pastes in formatting data. You can disable this by clicking on the “text only” box for the word that it is autocorrecting. You may also be able to make an exception for autocorrection, or perhaps just try to use a new symbol… not totally sure…