Local dev mixes extension and extension-less pages

[kptdobe]

Consider 2 different pages:

1. https://main--helix-perf-playground--adobe-rnd.hlx.page/test-cases/baseline: baseline gdoc page in gdrive
2. https://main--helix-perf-playground--adobe-rnd.hlx.page/test-cases/baseline.html: index.html static html file in github

When I run aem up and do the same locally:

1. http://localhost:3000/test-cases/baseline
2. http://localhost:3000/test-cases/baseline.html

both map to my local /test-cases/baseline.html

[ghost]

I don't understand this can someone help me out with this in a way I can understand