assetMap keys mysteriously also end up fingerprinted

Hi, I'm kind of lost looking for the origin of a specific problem. Any tips would be much appreciated!

# The problem
The asset map is supposed to be original file paths as **keys** and the fingerprinted file paths as **values**. However in my setup (`ember-cli@3.14` and `broccoli-asset-rev@2.7.0`) they are **both** fingerprinted, like this:

# Symptom
`assets/assetMap.json`
```
{
"assets": {
"assets/assetMap-0a44e35a1e3c8f7d9a47daebc0c9982d-70f2499612cdd7ad97c2c1ea906011ce.json": "assets/assetMap-0a44e35a1e3c8f7d9a47daebc0c9982d-70f2499612cdd7ad97c2c1ea906011ce.json",
"assets/assetMap-5bb51518a6cb320cc449d9cefeaa013b.json": "assets/assetMap-0a44e35a1e3c8f7d9a47daebc0c9982d-70f2499612cdd7ad97c2c1ea906011ce.json",
"assets/feedbackfruits-c3a921b164bc7b188050bd95294d81b9.css": "assets/feedbackfruits-c3a921b164bc7b188050bd95294d81b9.css",
"assets/feedbackfruits-c3a921b164bc7b188050bd95294d81b9.css-71651606cee8e5aaaee0a40e5cfe279c.map": "assets/feedbackfruits-c3a921b164bc7b188050bd95294d81b9.css-71651606cee8e5aaaee0a40e5cfe279c.map",
"assets/feedbackfruits-694083976caaef79ec066a43a11866ba.js": "assets/feedbackfruits-694083976caaef79ec066a43a11866ba.js",
"assets/feedbackfruits-ff41bb74ae0dc58507d8daee9b4e1e24.map": "assets/feedbackfruits-ff41bb74ae0dc58507d8daee9b4e1e24.map",
```

# Diagnosing
I've tried with various options on/off like `assetMapFingerprinting` or checking if `railsStyleManifest` maybe doesn't suffer from this (it also does). The related tests here still pass tho and checking a fresh ember CLI setup also doesn't display this, so it seems there's something to my setup that causes this.

Any ideas? Tips on how to further diagnose this would already help! :)