Schedule entry move or resize removes additional data

[terba]

Checklist

• I have updated to the latest available Home Assistant version.
• I have cleared the cache of my browser.
• I have tried a different browser to see if it is related to my browser.
• I have tried reproducing the issue in safe mode to rule out problems with unsupported custom resources.

Describe the issue you are experiencing

The additional data gets lost when a schedule entry is moved or resized. Tested on Firefox and Chromium on Linux, affects both.

Describe the behavior you expected

When moving or resizing a schedule entry the additional data entered by the user should remain unchanged.

Steps to reproduce the issue

1. Create an entry in a schedule via the UI (more-info cog icon)
2. Add an additional attribute to the entry
3. Move or resize the entry in the calendar view via dragging
4. The additional data is lost

What version of Home Assistant Core has the issue?

core-2025.1.1

What was the last working version of Home Assistant Core?

No response

In which browser are you experiencing the issue?

No response

Which operating system are you using to run this browser?

No response

State of relevant entities

No response

Problem-relevant frontend configuration

No response

Javascript errors shown in your browser console/inspector

No response

Additional information

No response