Using the code below on Qt for Embedded Linux 4.4.0 (also verified with 4.3.4), the dialog is painted with a weird frame in the bottom half. It might be related to the window flags.

//----------------------------------------------------------------------------
#include <QtGui>

int main( int argc, char * argv[] )
{
QApplication app( argc, argv );
QMessageBox msgBox;
msgBox.setFont( QFont( "DejaVu Sans", 12 ) );
msgBox.setWindowFlags( Qt::Dialog | Qt::CustomizeWindowHint );
msgBox.setStandardButtons( QMessageBox::Ok );
msgBox.setIcon( QMessageBox::Information );
msgBox.setWindowTitle( "Information" );
msgBox.setText( "It is not possible to delete the "
"actual selected model data!" );
return msgBox.exec();
}
//----------------------------------------------------------------------------