False Negative - Python `abc.ABC` makes method's `getACall` unavailable

If we have this Python code:
```python
class MyClass():
def method(self):
print("xxx")
def wrapper(self):
self.method()

mc = MyClass()
mc.method()
```
and this query:
```codeql
import python

from PythonFunctionValue method
select method.getACall()
```
It's OK that `self.method()` and `mc.method()` will be marked as positive.

However, those will be false negative as long as the class `MyClass` inherits `abc.ABC`. It looks like:
```python
from abc import ABC

class MyClass(ABC):
def method(self):
print("xxx")
def wrapper(self):
self.method()

mc = MyClass()
mc.method()
```

Why does the `abc.ABC` make the result wrong?