Back in KitKat, we were introduced to translucent system bars, which gave app developers the ability to make the navigation and status bars semi-transparent. Reclaiming as much of the screen as possible became an obsession for many fans as they demanded their favorite apps go "full bleed." With Android L, Google is treating us to even more flexibility by allowing developers to set their own color for the status bar, or even turning it completely transparent.
Earlier today, we noticed a bug report for a very strange issue with multiple user accounts on the Nexus 7. Apparently, certain applications are displaying the underlying screen - be it the wallpaper, app tray, or the Play Store (depending on where the app was launched from) - through the foreground app. But here's the kicker: it's only happening on secondary accounts. Yeah, it's confusing and strange.
There's also a Reddit thread that confirms this is happening, and it seems to only be affecting apps that call on some sort of transparency.