Virtual Keyboard causes Crash when Cancelling non-native QFileDialog

In our minimal example the Qt Virtual Keyboard is enabled in main.cpp. If this is enabled and the user dismisses a QFileDialog, there is a crash in the application. This crash does not always occur on the first dismissal but will happen soon after on subsequent dismissals ("Cancel"s).

The minimal code has a main window with a button to bring up a file dialog. Hit cancel on that file dialog when line 7 in main.cpp ( qputenv("QT_IM_MODULE", QByteArray("qtvirtualkeyboard")); ) is enabled. Comment out line 7 and there is no crash.

Some observations: if I run this code in the 5.8 beta release the file dialog is native to Ubuntu (gnome). In 5.7.0 it is showing a non-native Qt dialog with identical code. In 5.8 beta the virtual keyboard does not appear when trying to edit the native file dialog - this is suspected to be as designed. In the 5.7 non-native file dialog, the keyboard shows (again, as expected).