Screen curtain weirdness
I am running iOS 8.1.1 on an iPad Air. I just discovered something weird with the screen curtain. I have no idea how I managed to cause the issue, but it did get resolved after rebooting the iPad.
Normally, when I turn on the screen curtain, two things happen. First, the screen brightness is turned down to zero percent, although this is not reflected in the brightness indicator in the control center. The second thing the happens is that the screen is blackened, so that nothing is visible.
The problem I had is that, for some odd reason, turning on the screen curtain failed to blacken the screen. The brightness was still being turned down to zero, though. The result is that the the screen was still visible, albeit barely, when viewed in a dark room. Indeed, it looked exactly the same as it does when you turn the brightness down to zero percent in the control center but leave the screen curtain off. If I turned the brightness down to zero, there was no visible effect when toggling the screen curtain.
I discovered this when using the iPad in a room that was pitch dark, with no lights on. I have enough vision to determine if anything is being displayed on the screen, as well as some rough detail, such as if the app I'm using has a light or dark background. While having the screen curtain on, I noticed a glow from the iPad I was not used to seeing. The app I was using had a white background at the time. I hit the home button to go to the home screen, where I have a dark wallpaper configured, and I could clearly see the screen darken as the iPad switched to the home screen. I was even able to make out the animation which occurs during the transition.
Other effects I was able to make out included seeing a glow at the bottom of the screen while the control center was displayed, as well as the animation when using the app switcher. As I said above, the screen looked no different than it does with the brightness set to zero and the screen curtain off.
The problem went away after rebooting the iPad, after which the screen curtain now behaves normally, actually blackening the screen in addition to turning down the brightness.
I reported the issue to Apple Accessibility, but since I have no idea how I caused the issue to occur, or indeed how long it was going on before I noticed it, I doubt my report will be much help. I also don't know if this is an isolated fluke, or if it is something that others can cause to happen as well. I have a feeling that most VoiceOver users would have no idea if this issue was occurring on their devices.
Anyway, I thought this experience might be of interest to other people here.