You might've read about this issue in Phil's latest column, or experienced it first-hand if you've upgraded to Android 4.2 on a device with SwiftKey installed. In any case, some SwiftKey users are finding that after upgrading to the latest version of Android on Nexus devices, the keyboard is either soft-disabled or removed entirely, taking user data along with it in some cases.
Fortunately, SwiftKey says it's in touch with Google to identify exactly what's going on --
"This is a rare but unfortunate report that we've recently been made aware of. We have contacted the Android development team to understand what caused this in their code. We are doing what we can on our end to resolve this issue for those affected.
"Meanwhile, please redownload SwiftKey from the same storefront you originally purchased it from. As long as you are signed into the same account that you originally used to purchase the application, you will not be charged a second time. Also, remember that to get SwiftKey fully installed, you may need to click on the SwiftKey 3 icon in your app drawer to initialize the installation process."
It's rare to see this kind of glitch in a major OS update, but at least there's a simple workaround for those affected. And for what it's worth, SwiftKey works just fine on Android 4.2 once it's installed.