The reason, once I started doing some detective work, is simple. It's also something that could be easily fixed, while improving the lock screen's options. First though, see if you can guess what's going on...
Same time, same place, different channel...
As far as I can tell, the Bing lock screen is defaulting to the American image of the day, while the Bing search screen is using the UK image of the day. While there are some days when these two sync up, I'm invariably getting mismatches, or seeing an image on one area that was the surprise a few days ago.
Yes, it's a tiny problem, but I expect my mobile operating system, especially in the core apps, to have an attention to detail that's bordering on the obsessive. My guess is that the lock screen is outside of the 'regional coding' efforts that localise a handset to a region, while Bing is set up to include local searching based on your location. It wouldn't take much to tweak a fix into the next update of the OS.
- The lock screen image is pulled down using the same code and settings as Bing search.
- The lock screen settings screen gets an 'advanced' button which allows you to select the regional Bing image of the day to use.
Both of these would also take care of the 'updating at a different time' that can also put me off balance.
Yes, this is one of those classic #FirstWorldProblems, but Microsoft are coming from a long way back in the smartphone market space. They need to be laser focused on issues like this in Windows Phone 8, they need to be on a major bug hunt and making sure the user interface is consistent across the board, and they need to get these changes out as quickly as possible (just as Nokia do by using software installs for incremental patches and updates).
In short, Microsoft needs to constantly work to make sure Windows Phone 8 is always beautiful, welcoming, and understandable.