Some of the instructor privilege issues seem to have always been a bit sketchy with differing interpretations of the same reg - some of them being different depending on which part of the FAA you asked.

Just a sampling of those that have had support for varying views but have finally been "clarified" by FAR changes, Chief Counsel interpretations or both in recent years:

• Ground instructor can't give loggable flight training in a device.
• CFI-I with no aircraft instructor rating can't teach in any aircraft.
• CFI-A without an Instrument-Airplane rating cannot provide instrument training beyond the "flight solely by reference to instruments" training for the private certificate.
• Neither CFI nor trainee is a passenger, no neither needs to be landing-current.
• CFI ride does not reset the FR clock.
• CFIs may log trainee instrument approaches that occur in actual

Some parts of the FAA website are currently down but if you're interested, putting CFI or flight instructor in the search box at http://www.faa.gov/about/office_org/...terpretations/ should help you find all of them