I used the Find/Change function to change a particular word's format from "regular" to "bold" and within a numbered list where the Find/Change function applied, it changed the font of the number to a different font not used anywhere in the document.
Please show us a screen capture of the Find/Change dialog and the Change Formatting screen you get by clicking on the magnifier icon next to "change formatting" at the bottom of the dialog.You can embed screen shots in a post by using the camera icon on the web page like this: