Comment 6 for bug 1491034

Just to add in my findings from duplicate bug #1493872:

If the screen is locked after an application has been first opened unity doesn't remove focus from the app. It does remove focus on subsequent screen locks. This is what results in the keyboard not being dismissed if it was displayed prior to the screen being locked.

This can be seen in the application log (e.g. ~/.cache/upstart/application-legacy-messaging-app-.log), where you would expect to see the message:

UbuntuWindow::handleSurfaceFocusChange(focused=false)

Indicating that focus has been removed from the app, however this doesn't happen the first time you lock the screen after starting the app, only on subsequent locks.