We never update these properties after initializing an isolated object, so they become inaccurate when content / rows are added or removed.
<rdar://problem/91320204>
Created attachment 456762 [details] Patch
Created attachment 456771 [details] Patch
Committed r292564 (249402@main): <https://commits.webkit.org/249402@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 456771 [details].