The interlaced stereo modes aren't working since 2.78. To reproduce:
Using the default settings, from the default file:
- Check "Views" in the properties of "Render Layers"
- Press Num Pad "0" to view through the active camera
- An anaglyph stereo version of the scene is shown in the viewport
- From the "Info/Window" menu select "Set Stereo 3D" and change the display mode to "Interlace" (the interlace type of your choice)
- The viewport reverts to "mono" (shows only the left view). In 2.77 / 2.77a, an interlaced stereo was shown.