lmplot with refline produces unexpected markers on both ends of the lines

The following simple example which calls lmplot and then calls FacetGrid.refline produces some unexpected gray markers on both ends of the lines plotted by refline. This behavior seems specific to lmplot since those markers are not present when I use it with other plot types. This is on version 0.13.2

import seaborn as sns
import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({"x": [1.0, 2.0, 3.0], "y": [0.0, 1.0, 2.0]})
g = sns.lmplot(df, x="x", y="y")
g.refline(x=0, y=0)
plt.show()