Duplicate legend items when comparing energy data

[wilfredktlr]

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

When adding a section with an energy date selection card and energy devices detail graph card and then selecting the option to compare data the legend will also duplicate the legend items.

Describe the behavior you expected

The legend should only show the item once.

Steps to reproduce the issue

Create a new section with the code below. Select the Compare data option.

type: grid
cards:
  - type: energy-date-selection
  - type: energy-devices-detail-graph

What version of Home Assistant Core has the issue?

2025.3.1

What was the last working version of Home Assistant Core?

No response

In which browser are you experiencing the issue?

Google Chrome 133.0.6943.142

Which operating system are you using to run this browser?

Windows 11

State of relevant entities

Problem-relevant frontend configuration

Javascript errors shown in your browser console/inspector

Additional information

No response

[wilfredktlr]

This problem also applies to the main energy dashboard.