Issue Summary

This is reproducible on Data Center: yes

The bug appears in the Kanban/Scrum board setup where adding non-working days in the "Working days" section doesn't consistently function as expected. The highlighted current date requires an extra click for addition, and a similar issue arises when transitioning to the next or previous month

Steps to Reproduce

1. Go to Kanban/Scrum board configuration (Board needs to exist beforehand)
2. Go to the "Working days" section
3. Click "Add Date" button for Non-working days section
4. Choose date and click confirm
5. Click "Add Date" button for Non-working days section
6. Click prev/next month button (the date is still highlighted) / Leave the default highlighet date (current date)
7. Click confirm 

Expected Results

After confirmation, the date should be added. Only after clicking highlighted date once again, the date is added.

Actual Results

Highlighted date is not added without a manual click.

Workaround

Manually click highlighted date before clicking confirm.