The bug

If Framebuffer Objects are off, pressing the Super Secret Settings button causes the screen to go black. The screen will not reappear, even if shaders are turned off by pressing F4. It is not possible to see the screen again until the client is relaunched.

This also happens when spectating as a creeper, enderman, or spider (because a shader is applied). However, once left Shift (default) is pressed to return to free-flying mode, the screen returns to normal.

I have Framebuffer Objects off because the NVIDIA antialiasing I activated doesn't work unless it's off.

How to reproduce

1. Open options.txt in your .minecraft folder
2. Change the value of fboEnable to false
3. Save the file
4. Launch Minecraft
5. Open a world with cheats enabled or join a sever where you are opped
6. Enter spectator mode using /gamemode spectator
7. Find or spawn a creeper, spider, or enderman
8. Click on the mob to spectate it