I'm trying out Microbundle with https://github.com/reduxjs/redux-toolkit . For some reason, Microbundle seems to be ignoring the names that I've specified in the various main/module/exports fields, and is trying to reuse the the name from main for all output files.

Here's what I'm seeing. Currently, I've got package.json configured with these file names:

 "source": "src/index.ts",
 "main": "dist/a.js", 
 "exports": "./dist/b.modern.js",
 "module": "dist/c.module.js", 
 "unpkg": "dist/d.umd.js", 
 "types": "dist/typings.d.ts",

Microbundle reports this output:

Build "toolkit" to dist:
 7.22 kB: a.js.gz
 6.45 kB: a.js.br
 6.06 kB: a.modern.js.gz
 5.42 kB: a.modern.js.br
 7.14 kB: a.module.js.gz
 6.39 kB: a.module.js.br
 7.31 kB: a.umd.js.gz
 6.53 kB: a.umd.js.br

And the output files are:

dist/a.js
dist/a.modern.js
dist/a.module.js
dist/a.umd.js

Those are clearly not the file names I specified. Is there something obvious I'm missing here?