Currently, buffer-local-properties are reloaded each time the buffer is saved, overriding changes made by the user using the Buffer Options dialog. See an example use case at the bottom.
I think the right behavior during save is to prevent reloading of those buffer-local-properties that were changed by the user and whose buffer-local-properties haven't changed.
Example use case: The user guide of the Tags plugin (Tags/doc/users-guide.xml) is opened in 'rest' mode due to a buffer-local-property. This mode provides no syntax coloring for me, so I manually change it to XML using the Buffer Options dialog. As soon as I save the file after making changes to it, it automatically goes back again to 'rest' mode and again I lose the syntax coloring.