Reproduction steps:
1. Open the “ReproProject“ project
2. Open the “Assets/AnimatorController“ AnimatorController with a text editor application
3. Search for “AnimatorStateTransition“ in the text editor application
4. Observe the amount of “AnimatorStateTransition“ in the text editor application
5. Open the “Assets/AnimatorController“ AnimatorController in the Editor
6. Copy the “State 2” State in the Animator window
7. Paste the State in the Animator window
8. Save (File > Save)
9. Repeat steps 2, 3, 4

Expected result: The same amount of “AnimatorStateTransition“ is found in the AnimatorController file
Actual result: There is an additional “AnimatorStateTransition“ in the AnimatorController file

Reproducible with: 2021.3.37f1, 2022.3.24f1, 2023.2.18f1, 6000.0.0b14

Reproducible on: Windows 11 Pro (22H2)
Not reproducible on: No other environment tested

Notes:
Deleting the duplicated State in step 7 does not delete the additional “AnimatorStateTransition“ created in the Animator Controller file
Repeating the reproduction steps keeps creating new additional “AnimatorStateTransition“ in the Animator Controller file