Inventor stores styles in documents (local styles) and in the style library (library styles). The Use Style Library setting in the project determines whether styles in the style library are open for edit. The Read-Only status ensures that all style edits are kept in the local document.
In the lower pane of the Projects dialog box, confirm that the Use Style Library setting is Read-Only.
If it is set to Read-Write, right-click the setting, and select Read-Only. Then click Save.