I think you are seeing an existing problem with font style/sizes changing for no reason. At times, ME seems to revert to some small Arial font where a fixed font should be used. You will probably have to use the menu sequence Window -> Preferences -> General -> Appearance -> Colors and fonts -> Basic -> Text font. From there click the Use System Font, Apply, then Reset, Apply to restore the default fixed font.
If I’m not mistaken, users have reported the problem still exists with upcoming 7 release candidates, unfortunately.