Xperiodalignment not working for heatmap?

I might be doing something wrong, but I can’t get this to work. Any help would be greatly appreciated! Here’s a minimal example to make 3 heatmaps that seem like they ought to differ in their x-axis alignment, but do not.

import numpy as np
import pandas as pd
import plotly.graph_objects as go
from plotly.subplots import make_subplots

times = pd.to_datetime(list(range(10)), unit="s")
z=[[i for i in range(10)]]
z[0][4] = np.nan

fig = make_subplots(rows=3, cols=1)
fig.add_trace(go.Heatmap(x=times, z=z, xperiodalignment='start'), row=1, col=1)
fig.add_trace(go.Heatmap(x=times, z=z, xperiodalignment='middle'), row=2, col=1)
fig.add_trace(go.Heatmap(x=times, z=z, xperiodalignment='end'), row=3, col=1)