grabWindow get full white on osgEarth widget

My program has a main window with several widgets in it, one of which is the osgEarth widget, which shows the 3D Earth, and the map appears fine. I use QScreen::grabWindow to grab the main window of the application, and everything is fine except the osgEarth widget, which appears white.

I have tried:
gl_widget->setUpdatesEnabled(false);
QScreen::grabWindow(...)
gl_widget->setUpdatesEnabled(true);

But not work, The osgEarth area in the grab result is always white. I have test the PrintScreen key is fine. How can I solve this problem? Thanks.