"QtObject" C++ class breaks Qt global object in QML

Steps to reproduce:

1. Create Qt Quick application using Qt Creator.
2. Add a new QObject-derived class and name it as "QtObject".
3. Build and run. Result: you can't call any methods of Qt object in QML. QML produces errors like main.qml:9: TypeError: Property 'size' of object QtObject(0x6519b095ff10) is not a function.

Works fine under Windows/macOS/Android. It's a Desktop Linux-only issue.