If I change the categories on an article but do nothing else, saving it doesn't mark them as saved so if I try to quit OLW or open a different article, it tells me I have unsaved changes.

Repro:

1. Create an article and save it.
2. Change the categories and nothing else. Click save.
3. Without making any further changes, try to close the OLW window. You will be told you have unsaved changes and asked if you want to save them.

This happened with WLW as well.