Assigning a new QObject w/o a parent to a C++ property through QML doesn't prevent it from being garbage collected

Qt 5.13.1 (x86_64-little_endian-lp64 static release build; by Clang 10.0.0 (clang-1000.11.45.5) (Apple)) on "cocoa" 
OS: macOS Mojave (10.14) [darwin version 18.7.0]

Architecture: x86_64; features: SSE2 SSE3 SSSE3 SSE4.1 SSE4.2 AVX AVX2 RTM HLE

Environment:

Features: QT_NO_EXCEPTIONS QT_NO_OPENSSL

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Network:
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Theme:
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LibGL Vendor: ATI Technologies Inc.
Renderer: AMD Radeon Pro 580 OpenGL Engine
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Shading language: 1.20
Format: Version: 2.1 Profile: 0 Swap behavior: 2 Buffer size (RGB): 8,8,8
Profile: None (QOpenGLFunctions_5710346_1)