The current implementation of QApplication::setInputContext is wrong:

void QApplication::setInputContext(QInputContext *inputContext)
{
    Q_D(QApplication);
    Q_UNUSED(d);// only static members being used.
    if (!inputContext) {
        qWarning("QApplication::setInputContext: called with 0 input context");
        return;
    }
    delete d->inputContext;
    d->inputContext = inputContext;
}

If d->inputContext already pointed to the same instance as inputContext, then it'll assign a dangling pointer to d->inputContext, which can easily crash the application.

So what's wrong:

• No guard against self-assignment,
• After calling delete, d->inputContext should be set to 0 (or, d->inputContext should be wrapped in a QPointer),
• Since QInputContext can be parented, it is questionable whether this setter should delete anything at all - The documentation does not mention this behaviour (to "replace" an object is not necessarily the same as destroying it).

(selected "text handling" since QInputContext is a text input helper)