Does customdata/hovertemplate not work with Histogram2d? (with MRE and Screenshot)

Iā€™d have expected to be able to include the customdata (list/pandas series) into the hovertemplate, but this is not appearing as intended. The literal text %{customdata} appears instead.

import plotly.graph_objects as go
import numpy as np
import pandas as pd

x = np.random.randn(500)
y = np.random.randn(500) + 1
z = np.random.randn(500) + 2
a = np.random.randn(500) + 4

fig1 = go.Figure(
    go.Histogram2d(
        x=x,
        y=y,
        z=z,
        customdata=a,
        hovertemplate="%{a[0]}"
    )
)

fig1.show()