Date field change date on focus to +1 month and +1 year

I configured the date field as follows:

    label: Ablaufdatum
    type: date
    format: MM.YYYY
    display: MM.YYYY
    default: today

After selecting a date (by calendar or manual input) then saving and clicking on the field again, the date changes to 08.2023. The error does not occur when I set display: DD.MM.YYYY. Any suggestions how to solve this problem or is it a bug?

Kirby v3.7.1