Input context disappears during reparenting

My goal is to develop a virtual keyboard for a line edit with the help of a QInputContext. So, I wrote an input context plugin, which you find in the directory VirtualKeyboardPlugin of the attached tarball. Then, I wrote a simple app found in the directory VirtualKeyboard; PhoneNumberWidget is the class of interest.

In the ctor of PhoneNumberWidget, I assign a virtual-keyboard input context to a line edit:
m_edit0 = new QLineEdit;
m_edit0->setAttribute(Qt::WA_InputMethodEnabled);
m_edit0->setInputContext(QInputContextFactory::create("VirtualKeyboardContext", m_edit0));

I add the widget to a grid layout
QGridLayout *grid = new QGridLayout;
grid->addWidget(label0, 0, 0);
grid->addWidget(m_edit0, 0, 1);
which I add to a vbox layout:
QVBoxLayout *vbox = new QVBoxLayout;
vbox->addLayout(grid);

Finally, I set the top-level vbox layout on "this" widget:
setLayout(vbox);

The function setLayout() sets the input context of the line edit to 0, that is, m_edit0->inputContext() returns 0 after setLayout() and returns the right value before. The stack trace shows this:
#0 0x00f51931 in QMetaObject::changeGuard (ptr=0x80b6a5c, o=0x0)
at /home/stubert/Development/Qt-4.7.0/releases/src/corelib/kernel/qobject.cpp:472
#1 0x00322424 in QPointer<QInputContext>::operator= (this=0x80b6a5c, p=0x0)
at ../../include/QtCore/../../../releases/src/corelib/kernel/qpointer.h:68
#2 0x003707f3 in QWidgetPrivate::setParent_sys (this=0x80b69e0, parent=0xbffff2ac, f=...)
at /home/stubert/Development/Qt-4.7.0/releases/src/gui/kernel/qwidget_x11.cpp:1273
#3 0x0031ad79 in QWidget::setParent (this=0x80c4108, parent=0xbffff2ac, f=...)
at /home/stubert/Development/Qt-4.7.0/releases/src/gui/kernel/qwidget.cpp:9950
#4 0x0031aad8 in QWidget::setParent (this=0x80c4108, parent=0xbffff2ac)
at /home/stubert/Development/Qt-4.7.0/releases/src/gui/kernel/qwidget.cpp:9907
#5 0x002e4b5b in QLayoutPrivate::reparentChildWidgets (this=0x80c91e0, mw=0xbffff2ac)
at /home/stubert/Development/Qt-4.7.0/releases/src/gui/kernel/qlayout.cpp:972
#6 0x002e4d65 in QLayoutPrivate::reparentChildWidgets (this=0x80b5f28, mw=0xbffff2ac)
at /home/stubert/Development/Qt-4.7.0/releases/src/gui/kernel/qlayout.cpp:976
#7 0x0031a241 in QWidget::setLayout (this=0xbffff2ac, l=0x80d2a38)
at /home/stubert/Development/Qt-4.7.0/releases/src/gui/kernel/qwidget.cpp:9594
#8 0x0804bb5b in PhoneNumberWidget (this=0xbffff2ac, parent=0x0) at phonenumberwidget.cpp:45
#9 0x0804ad59 in main (argc=1, argv=0xbffff394) at main.cpp:8

The problem is line 1273 in qwidget_x11.cpp (QWidgetPrivate::setParent_sys), where the input context ic is set to 0 (ic = 0.

For sure, this is the wrong behaviour. Reparenting must not remove the input context that was explicitly set before.

Moreover, this line also introduces a memory leak. The input context set earlier is never deleted (destructor of VirtualKeyboardContext is never called).

How to build the attached example:

• Unpack the tarball
• cd VirtualKeyboardPlugin; qmake; make
• cd ../VirtualKeyboard; qmake; make
• in VirtualKeyboard run ./VirtualKeyboard