This is a regression in the refactored platform plugin, because it does not happen with Qt 5.2.1.
1. Create a Qt Widgets application in Qt Creator
2. Run it
3. Hit the home button to suspend it
4. Use the "recent application list" to re-open it.
Before, the application would pop back up, but with a current build of Qt 5.3.0, it will only show a black screen. Changing orientation on the device does not help.
Using the application launcher to restore the app yields the same results.
This was reproduced on a Nexus 5 with Android 4.4.2.