I wanted to use the "Config File Provider plugin" to specify and reuse a maven settings.xml (Maven builder -> Settings file -> provided settings.xml). Everything seemed to work ok until i reopened the project's configuration page and stored the project: Now the specified settings.xml was lost! I made a copy of the project's config.xml before and compared it. The "settingsConfigId" element became empty, everytime i saved the project. It is only stored when i explicitly set the "provided settings" to use.
This is very awkward, especially because the "Settings file" part is not seen right away when you open the project's configuration page.