`geom_segment` with `arrow` in `facet_grid` produces strange arrow heads

[mnicstruwig]

Reproducible example (plotnine == 0.6.0):

from plotnine import *
import pandas as pd


df = pd.DataFrame({
    'x': [1, 2],
    'xend': [3, 4],
    'y': [10, 10],
    'yend': [9, 9],
    'facet': ['a', 'b']
})

p = ggplot(aes(x='x', xend='xend', y='y', yend='yend'), df)
p = p + geom_segment(arrow=arrow()) + facet_grid('~ facet')
print(p)

which produces the following plot with weird arrow heads:

The issue also occurs when using annotate instead of geom_segment directly.

If facet_grid is not used, the issue disappears (which makes me suspect it's got something to do with the axes' scale, but I'm very unfamiliar with the internals of plotnine).

Thanks!

[mnicstruwig]

Fantastic, thanks for the quick turnaround!