Why do stylesheets influence QTableWidget behaviour?

Question

I use python2.7 and PyQt4. I created a simple app with a button-box and a table-widget. If I edit a table cell and press the Ok button, the cell editor always disappears. But after I add the app.setStyleSheet(s) line, the cell editor does not disappear after the OK button is pressed. What is going on?

import sys
from PyQt4 import QtGui


class Widget(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)

        l = QtGui.QVBoxLayout(self)

        table = QtGui.QTableWidget()

        table.setColumnCount(3)
        table.setRowCount(5)

        l.addWidget(table)

        l.addWidget(QtGui.QDialogButtonBox(QtGui.QDialogButtonBox.Ok | QtGui.QDialogButtonBox.Cancel))


if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    s = "QWidget{background:red;}"
    # app.setStyleSheet(s)
    app.setStyleSheet(s)

    mw = QtGui.QMainWindow()
    w = Widget()
    mw.setCentralWidget(w)
    mw.show()

    sys.exit(app.exec_())

Answer 1

This seems to be a bug in Qt4, but I can't find a specific report for it. The same code works as expected when using PyQt5, so it somehow got fixed at some point.

The bug is actually in QDialogButtonBox rather than QTableWidget. If you add a QLineEdit to the example and set focus on it, you will see that clicking on the Ok button does not switch focus. Or to be more precise, clicking on the first button does not switch focus. All the other buttons in the button-box work normally.

I thought that this might have something to do with the default and/or autoDefault properties, because they usually change the way buttons are styled (e.g. a highlighted border). But setting the properties doesn't have any effect - the bug really does seem to affect just the first button.