Is there a bug in the library of altair?

Hi guys,

I do not know whether the problem should be asked about in the Streamlit community.

I am using altair to draw the diagram but it seems to exist a wrong text by applying stack data.

Here is my partial code:

bars = alt.Chart(df).mark_bar().encode(
    x=alt.X('Quantity:Q', stack='zero', axis=alt.Axis(title='Quantity', tickMinStep=1)),
    y=alt.Y('Time:N'),
    color=alt.Color('User')
)

text = alt.Chart(df).mark_text(dx=-10, dy=0, color='white').encode(
    x=alt.X('Quantity:Q', stack='zero'),
    y=alt.Y('Time:N'),
    detail='User:N',
    text=alt.Text('Quantity:Q', format='d')
)
st.altair_chart(bars + text, use_container_width=True)

As you can see, the upper text is correct, but the lower text is exchanged.
Sometimes it is correct, but sometimes it is not correct in this diagram.
Is there any idea about it?

Thank you!

BR,
Chieh