overflow-y: hidden areas can still be scrolled by selecting and dragging text. This doesn't reproduce if you set overflow hidden in both directions though.
Created attachment 187964 [details]
Sounds like related to bug 104373 .
I had a patch to it, but had to revert because of some unforeseen test failures: https://trac.webkit.org/changeset/136954
Let me know if it is the same, as I got a revised patch ready, please.
Yes, this issue looks to be a duplicate of https://bugs.webkit.org/show_bug.cgi?id=104373.
*** This bug has been marked as a duplicate of bug 104373 ***