[BUG] dcc.DatePickerRange class removed for first date after max_date_allowed

[rzvcs]

Describe your context
I use dcc.DatePickerRange and max_date_allowed with CSS override of class CalendarDay__blocked_out_of_range to set a background for the dates beyond maximum. This helps our UX well. However, using the calendar to select a new range removes this class for the next date after max_date_allowed.

• replace the result of pip list | grep dash below

dash                 3.2.0

• if frontend related, tell us your Browser, Version and OS

  • OS: Windows 11 24H2 26100.6584
  • Browser: Chrome
  • Version: 140.0.7339.128

Describe the bug

Using dcc.DatePickerRange with max_date_allowed sets css class CalendarDay__blocked_out_of_range for days beyond the max_date_allowed. When clicking on a new start or end date in the calendar, the class is removed for date == max date allowed. Closing the calendar and opening it again repeats the whole behaviour.

Use sample code in main.py:

from datetime import date
from dash import Dash, html, dcc

app = Dash(
    assets_folder="./assets"
)

STRFORMAT = "%Y-%m-%d"
app.layout = [
    html.Div(
        children=[
            'Repro', 
            dcc.DatePickerRange(
                start_date=date(2025,9,21).strftime(STRFORMAT),
                end_date=date(2025,9,25).strftime(STRFORMAT),
                max_date_allowed=date(2025,9,26).strftime(STRFORMAT),
                display_format='YYYY-MM-DD',
                id="my-date-range-picker",
                updatemode="bothdates"
            )
        ]
    )
]

if __name__ == '__main__':
    app.run(debug=True)

Create a folder assets at main.py location and add style.css:

.CalendarDay__blocked_out_of_range {
    background-color: rgba(240, 240, 240, 1) !important;
}

Expected behavior

CSS Class should still be enforced.

Screenshots
Open the calendar picker and the 27th has the class applied:

Click on a new date and the 27th doesn't have the class applied:

[Farkites]

This issue is fixed with dash==4.0.0rc3