Press ← button in Windows Phone 8.1 does not actually close Qt app

[jiangcaiyang]

I tested some Qt programs under Windows Phone 8.1, and found that when I press left( ← ) button and Qt app does not actually close itself, I pressed and held the button and the screenshots of the "closed" Qt application are still shown. Other programs not using Qt does not appear to have this phenomenon.

[jiangcaiyang]

This bug report is something like my problem.
https://bugreports.qt-project.org/browse/QTBUG-41946