useFetcher and fetcher.submit in child component trigger unexpected parent (route) component re-render

[fonzcastellanos]

Reproduction

Go to https://stackblitz.com/~/github.com/fonzcastellanos/react-router-use-fetcher-bug, enter a non-empty string to the "Message" input field, and press the "Submit" button.

Note that StrictMode is disabled.

System Info

System:
    OS: macOS 15.5
    CPU: (14) arm64 Apple M3 Max
    Memory: 1.61 GB / 36.00 GB
    Shell: 5.2.21 - /opt/homebrew/bin/bash
  Binaries:
    Node: 20.9.0 - ~/.nvm/versions/node/v20.9.0/bin/node
    npm: 10.1.0 - ~/.nvm/versions/node/v20.9.0/bin/npm
  npmPackages:
    @react-router/dev: ^7.5.3 => 7.6.3 
    @react-router/node: ^7.5.3 => 7.6.3 
    @react-router/serve: ^7.5.3 => 7.6.3 
    react-router: ^7.5.3 => 7.6.3 
    vite: ^6.3.3 => 6.3.5

Used Package Manager

npm

Expected Behavior

I expected the Parent route component to not re-render, while the Child component would re-render as a result of calling fetcher.submit, which submits to the /resource resource route that defines only an action.

Actual Behavior

The Parent route component re-rendered unexpectedly. After the handlerSubmit function executed (which calls fetcher.submit), both the Parent and Child components re-rendered.

This is the browser console output.

This is the terminal output from the dev server. "hello world" was the string I entered into the "Message" field.

[fonzcastellanos]

The following issue may be the same: #13851