I suspect this regressed when the uncovered inactive tab color was made darker. IMO, it is too dark now.
Will address in <https://webkit.org/b/199023>.
*** This bug has been marked as a duplicate of bug 199023 ***
As it turns out, <https://webkit.org/b/199023> was just my mouse moving too quickly and triggering some hover styling.
Created attachment 372488 [details]
Created attachment 372489 [details]
[Image] After Patch is applied
Comment on attachment 372488 [details]
Clearing flags on attachment: 372488
Committed r246666: <https://trac.webkit.org/changeset/246666>
All reviewed patches have been landed. Closing bug.