Belchertown: xAxis_groupby with time_length = years_ago does not work

[Matthias Manhart]

I would like to show my pv energy by year:

[eyear]
    show_button = true
    button_text = "Jahr"
    title = "Jahr"
    time_length = year
    tooltip_date_format = "LLLL"
    gapsize = 2678400000               # 31 Tage in [ms]
    yAxis_label = "Energie"
    start_at_midnight = true
    start_at_beginning_of_month = true
    xAxis_groupby = month
    xAxis_categories = 'Jan', 'Feb', 'Mar', 'Apr', 'Mai', 'Jun', 'Jul', 'Aug', 'Sep', 'Okt', 'Nov', 'Dez'

    [[energy_plt]]
        title = "Energie"
        [[[pv_day_wh]]]
            name = PV
            color = "#ffc83f"
            type = column
            unit = kilowatt_hour

    [[energy1_plt]]
        title = "Energie 2021 [A]"
        year_specific = 2021
        [[[pv_day_wh]]]
            name = PV
            color = "#ffc83f"
            type = column
            unit = kilowatt_hour

    [[energy2_plt]]
        title = "Energie 2021 [B]"
        time_length = years_ago
        time_ago = 1
        [[[pv_day_wh]]]
            name = PV
            color = "#ffc83f"
            type = column
            unit = kilowatt_hour

Live view: https://www.beathis.ch/weewx/energy/?graph=eyear

The chart [A] is correct, but i had to use ' year_specific = 2021 '. Chart [B] is using ' time_length = years_ago ' and it seems, that this chart is collecting all data from every month in the path and not only from 2021.

I would like to use ' time_length = years_ago ' for this chart. Any idea how ?

Regards

Matthias