Webview radio button and checkboxes missing

Similar to RT-28671, WebView does not show all checkboxes/radiobuttons. This is not fixed as indicated by that ticket but reproducible with 8.0 b118 on Mac

Steps to reproduce:
1. Start testcase in comment below.
2. Scroll vertically.

Expected: all controls visible
Actual: some controls missing their button area

When increasing window size the problem becomes more apparent. It seems as if the number of simultaneously visible controls is limited to about 100. With a bigger window size more controls need to be displayed, but that does not happen.

I would reopen RT-28671 but am not allowed to do so anymore.