[O] indentation error in python source block

[Seb]

Hello,

I believe I've hit a strange bug.  Given this file:

---<--------------------cut here---------------start------------------->---
#+STARTUP: content indent hideblocks
#+PROPERTY: header-args :tangle yes
#+PROPERTY: header-args:python :session *Python*

#+NAME: python_init
#+BEGIN_SRC python :results silent :exports none
import matplotlib as mpl
mpl.use("Agg")
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
#+END_SRC

#+NAME: test
#+BEGIN_SRC python :results file :exports results
beg = ["2017-07-13 15:27:31", "2017-07-13 15:28:24"]
beg = pd.to_datetime(beg)
end = ["2017-07-13 15:28:03", "2017-07-13 15:28:57"]
end = pd.to_datetime(end)
pos = np.arange(1, 3).tolist()
experiment = pd.DataFrame(dict(index=np.arange(1, 3),
                               beg=beg, end=end, pos=pos))
# Mid points
experiment["mid"] = (experiment["beg"] +
                     (experiment["end"] - experiment["beg"]) / 2)
fig, axs = plt.subplots(3, 1, sharex=True)
# Shade experiment periods
for idx, row in experiment.iterrows():
    for ax in axs:
        ax.axvspan(row["beg"], row["end"], facecolor="0.5")
    axs[0].annotate(row["pos"], (row["mid"], 1), ha="center",
                    xycoords=("data", "axes fraction"))
# TEMPORARY: limit to experiment periods
axs[0].set_xlim(experiment["beg"].iloc[0],
                experiment["end"].iloc[-1])
fig.tight_layout()
fig.savefig("junk.png", bbox_inches="tight")
plt.close()
"junk.png"
#+END_SRC
---<--------------------cut here---------------end--------------------->---

Problem is in the second source block.  With point on the #+BEGIN line,
hitting C-c to execute the block yields indentation errors in the
Python process (first one):

---<--------------------cut here---------------start------------------->---
>>>                 experiment["end"].iloc[-1])
  File "<stdin>", line 1
    axs[0].annotate(row["pos"], (row["mid"], 1), ha="center",
    ^
IndentationError: unexpected indent
---<--------------------cut here---------------end--------------------->---

Tangling the file and running the Python script shows no error at all.
Executing the source block from the dedicated buffer via C-c '
(`org-edit-special') also runs without errors.  What is going on?

Thanks,
-- 
Seb