Short description of error
If you render (or create a new window that is not a Main Window you don't see the menu to change the stereo mode.
Exact steps for others to reproduce the error
(based on the original report, though saving and re-loading is a bit irrelevant here)
Open blender with a camera pointing at a camera
Go into scene view and turn on;
- Stereo 3D mode (not Multi-View)
- Views > Stereo 3D (not individual)
Do a test render and notice how the blender render window shows anaglyph fine.
Switch to a different stereo mode e.g., Interlace and notice how the render still displays an anaglyph image.
The stereo setting of the main window doesn't get shared between the children windows.