Blank square on full screen start up

[taxen]

At least since 1.2.4 (through 1.2.6), a white blank square shows up on full screen start up.
I bumped up from 1.1.8 to 1.2.4, so I do not know when it started.
The square is not harmless, but it seems to take some time for it to be displayed.
Is there a way to suppress it? I looked around the options in vein.

[kanryu]

This bug has already been confirmed and fixed.
In previous versions, it would be displayed for a longer period of time, especially when launched with an image file specified.

The above screen shot now appears for just a moment, but this will be resolved quickly and should not cause any problems in practice.
This is essentially a bug specific to Qt6, and even though you call MainWindow::showFullScreen() after ImageView::resetBackgroundColor(), the original Win32SDK window and its background, which Qt does not draw, will be displayed for just a moment. It appears that this behavior cannot be prevented.
As this occurred in Qt6 and not in Qt5, we believe it is a Qt6 bug.