Since QFont style hints won't work on X11, we force the font to fixed pitch if the family isn't set

src/mainwin.cc

@@ -1801,6 +1801,7 @@ void MainWindow::setFont(const QString &family, uint size)
 {
 	QFont font;
 	if (!family.isEmpty()) font.setFamily(family);
+	else font.setFixedPitch(true);
 	if (size > 0)	font.setPointSize(size);
 	font.setStyleHint(QFont::TypeWriter);
 	editor->setFont(font);