Patch.Append recreate existing DOM nodes? #3945

Hi, thank you so much for creating Dash. I’ve really enjoyed using it, and it has been the foundation for one of my own projects.
While investigating a performance issue in my application, I noticed what seems to be a behavioral change between Dash 4.1.0 and 4.2.0. I may be misunderstanding how Patch.Append is intended to work, so I wanted to ask whether this behavior is expected.

Describe your context
pip list | grep dash
dash 4.3.0

• OS: macOS Tahoe 26.5.2
• Browser: Google Chrome 151.0.7922.77 (arm64)
• Python: 3.12.10

Describe the bug
In my test, a callback returns only a root-level Patch.Append to append one child. The existing child is not returned or replaced.
With Dash 4.1.0, the existing DOM node is preserved.
With Dash 4.2.0, the existing DOM node appears to be disconnected and recreated.
I first noticed this while investigating my own application, and then reproduced the same behavior in a small standalone example.
Dash 4.1.0
{
"same": true,
"beforeConnected": true,
"afterConnected": true,
"childCount": 2
}
Dash 4.2.0
{
"same": false,
"beforeConnected": false,
"afterConnected": true,
"childCount": 2
}

Expected behavior
I expected a tail Patch.Append to preserve the existing child DOM node and only create the newly appended child.
If I’m misunderstanding the intended semantics of Patch.Append, I’d really appreciate any clarification.

Thank you.