[Bug]: Default export of library is undefined in final build

[natocTo]

System Info

System:
- OS: macOS 14.5
- CPU: (11) arm64 Apple M3 Pro
- Memory: 1.26 GB / 18.00 GB
- Shell: 5.9 - /bin/zsh

Binaries:
- Node: 20.15.1 - /opt/homebrew/bin/node
- Yarn: 1.22.22 - ~/Documents/GitHub/ui/node_modules/.bin/yarn
- npm: 10.2.3 - ~/Documents/GitHub/ui/node_modules/.bin/npm

Browsers:
- Chrome: 129.0.6668.89
- Safari: 17.5

Details

I am migration one library from Webpack do Rspack. Locally (dev) working great, I have a issue with final production build.

Related config:

library: { name: 'kbcApp', export: 'default', type: 'window' },

Related default library export:

export default {
  start: startApp,
  helpers,
};

Check final export from compilted files:

There is "collision" in names - Z and default. I am not sure why it is Z in the object, but it is not reflected bellow.
The s.default return undefined, when I override it to s.Z it works as expected.

Am I doing something wrong?

Reproduce link

No response

Reproduce Steps

1. build library with default export
2. check final build if library is correctly assigned