Difference in Accept-Language and navigator.languages

Question

According to MDN doc,

The Accept-Language HTTP header in every HTTP request from the user's browser uses the same value for the navigator.languages property except for the extra qvalues (quality values) field (e.g. en-US;q=0.8).

and spec

To avoid introducing any more fingerprinting vectors, user agents should use the same list for the APIs defined in this function as for the HTTP Accept-Language header.

while adding en-US without en language, two values are different.

navigator.languages

['en-US']

accept-languages

en-US,en;q=0.9

I am using Microsoft Edge Version 103.0.1264.49 (Official build) (64-bit)

Is this a normal behavior or it's a bug of microsoft edge?

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I have even tested in the latest chrome and firefox.

chrome behaves exact the same as edge because they are using the same engine.

Firefox is working perfect and same as the doc stated. Accept-Language and navigator.languages are the same.

it seems it is a bug of chromium.