Segfault when calling unknown method on PyObject

[mre]

pyo3 version: 0.2.6
Operating System: MacOS 10.12.6

Trying to execute a non-existent method on a PyObject causes a segmentation fault.
I expected an AttributeError just like it's the case when calling a non-existent method on a &PyObjectRef.

extern crate pyo3;
use pyo3::{ObjectProtocol, PyObject, PyObjectRef, PyResult, Python};

fn main() {
    let gil = Python::acquire_gil();
    hello(gil.python()).unwrap_or_else(|e| e.print(gil.python()));
}

fn hello(py: Python) -> PyResult<()> {
    let io = py.import("io")?;
    let sio: &PyObjectRef = io.getattr("StringIO")?;

    // This works (throws an AttributeError as expected)
    // Comment this line to reproduce the segfault
    sio.call_method("asdf", (0,), pyo3::NoArgs)?;

    let sio_obj: PyObject = sio.into();
    // Segfault happens here:
    sio_obj.call_method(py, "asdf", (0,), pyo3::NoArgs)?;
    Ok(())
}