I've attached a reproduction case. Here's the setup.py that I used:

```
from distutils.core import Extension, setup

extension = Extension("breaky", ["breaky.c"])

setup(
    name="tp_clear",
    version="0.1.0",
    ext_modules=[extension],
)
```

which I built and ran with:
```
python setup.py build_ext --inplace
python -c "import breaky, gc; a = breaky.Breaky(); a = 1"
```