Invalid output produced

[unconfident]

Having font-variant set to initial before font-feature-settings property somehow corrupts produced output for font-feature-settings.

Input:

.this-will-be-broken {
   font-variant: initial;
   font-feature-settings: normal;
}

.this-will-not {
  font-variant: normal;
  font-feature-settings: normal;
}

Expected output

Should match the input one to one

Produced output:

.this-will-be-broken {
   font-variant: initial;
   font-feature-settings: normal, ;
}

.this-will-not {
  font-variant: normal;
  font-feature-settings: normal;
}

Observing this on version 4.0.1 but saw the same happen nearly a year ago, before 4.0.1 was released, so I guess at least 4.0.0 is affected as well.

[unconfident]

It took me 2.5 hours to narrow it down to this package. Would have probably been much easier if you had an interactive playground like the ones Typescript and Babel have. I looked around but couldn't find one.

How are you normally triaging issues likes this in the postcss ecosystem?