Multi-day conferences - contributions scheduled on the later days are scheduled incorrectly
For example: when adding Contributions to Day 2 of a multi-day conference, Indico:

1. gives the following notification - Event start time changed to 4:00 am.
2. places the Contribution meant for Day 2 on Day 1 at 4:00 a.m.
3. changes the Start time (in Settings) of the entire conference to 4:00 am.

Video of the issue:

Steps to Reproduce:

1. Create multi day conference:  e.g. September 13, 2024 to September 16, 2024, 9:00 am to 4:00 pm
   

2. Create several contributions
3. Go to Timetable

4. Go to Day 1, Friday, September 13, 2024
   

5. Go to Add new and select Contribution – a contribution is added as expected at 9:00 am
6. Go to Day 2 in the timetable, Saturday, September 14, 2024
7. Go to Add new and select Contribution - at this point the user sees the Notification = “Event start time changed to 4:00 a.m.” and the Contribution is placed in the Timetable on Friday, September 13, 2024, at 4:00 am. As well, in event Settings – Start has been changed by Indico to 4:00 am as per the above notification

Expected behaviour:
I expect my Contribution to be placed in the Timetable on the date I call them from, e.g. if I am on Day 2 in the timetable, the contribution should be placed in Day 2. Also, I would never expect Indico to change the Start date of my conference.

Screenshots:

Additional context
We tested this in your demo environment and we were able to reproduce this issue.