[Challenge] When you change the start date of the challenge, the calendar does not display the last saved date

[CUDO1]

Environment: Win 10 OS, Google Chrome
Reproducible: always

Preconditions

1. Go to - https://speak-ukrainian.org.ua/dev/
2. Click on avatar
3. Click on "Увійти"
4. Login with admin credentials:
   [e-mail] | admin

Steps to reproduce

1. Click on the avatar
2. Hover to "Контент"
3. Hover to "Челенджі"
4. Click on "Челенджі"
5. Click on challenge "Ukrainian" (ID:857)
6. Click on "Змінити дату старту"

Actual result

When you change the start date of the challenge, the calendar does not display the last saved date

Expected result

The calendar should display the last saved date

User story and test case links
E.g.: "User story #1737