QML Preview + VirtualKeyboard == 2 QML engines available

After showing Qt Virtual Keyboard for the first time during QML Preview session, preview can not be updated anymore. Error message in console says:

Error loading QML Live Preview:
2 QML engines available. We cannot decide which one should load the component.

1. It is obviously a Qt bug — Qt / QML / Creator can not handle things they were designed for.
2. There should be some way to distinguish QML engines, in case if there are many of them. How did it happened that Qt Creator used a socket to connect, but both engines ended up replying on it?

Steps to reproduce:

1. Start new Qt/QML project
2. Add a QtQuick.Controls/TextField component
3. Install Qt Virtual Keyboard module
4. Add QT_IM_MODULE=qtvirtualkeyboard environment variable, for example before initializing app in C++:
   qputenv("QT_IM_MODULE", QByteArray("qtvirtualkeyboard"));
5. Start QML Preview
6. Make changes to the document to make sure live reloading works
7. Click on a text field to active keyboard
8. Make changes to the document again. It should produce errors from now on.