Drawing an arrow didn't work properly if you

pizzathief · pizzathief · commit 794a2e3f1fab · 2015-11-01T09:27:07.000+11:00
had the instructions for drawing the left part, and
the right part, concatenated the two, without
chopping off enough of the left part instructions.
diff --git a/lib/matplotlib/patches.py b/lib/matplotlib/patches.py
@@ -1203,7 +1203,7 @@ def __init__(self, x, y, dx, dy, width=0.001, length_includes_head=False,
                     # The half-arrows contain the midpoint of the stem,
                     # which we can omit from the full arrow. Including it
                     # twice caused a problem with xpdf.
-                    coords = np.concatenate([left_half_arrow[:-1],
+                    coords = np.concatenate([left_half_arrow[:-2],
                                              right_half_arrow[-2::-1]])
                 else:
                     raise ValueError("Got unknown shape: %s" % shape)
