The problem may [at least partially] go back to MSWord.
In MSword I created 2 list styles bltStyl1, bltStyl2, and applied the styles to different bullets in the document. When I then change one of the styles bltStyl1 by changing the bullet character and apply this style to a bullet that formerly had style bltStyl2, several of the bltStyl2 bullets change their bullet character leading me to speculate that word may be attempting to change the style of all of the bullets it infers to be items of the same list, but it does not do so in a consistent and well defined way.
By way of background, for the example I sent in, when I first created the document, the custom bullet style "JBullet" used for the bullet character, a wingding character consisting of an empty square. I later modified this style to use the filled square wingding character. In MSWord the style appears correctly, but the old style definition seems to be retained in the document and some of the manipulation of the document by Aspose.Words seems to have made the JBullet style revert to using the earlier style definition character [empty square], though in theory, a bullet/list style using the empty square no longer exists. I can't find a documented way to excise the earlier style definition though I would have expected that modifying the style should have removed any history of the earlier style anyway.
Hope this helps in tracking down a solution.