Web view freezes with dev tools open

On 6.9.0 beta3 (commit c2fcaa282095c in the top level Qt repo) when the dev tools are open and attached to a web view one or the other of the web view or inspector window will stop updating until you resize the frozen window.

You can reproduce this in Simplebrowser like so:

1. open up a web page with the following requirements (eg https://en.wikipedia.org/wiki/List_of_lists_of_lists):
   1. long enough to you can scroll the content up and down (to check if changes to the page are being drawn)
   2. links you can hover over to see the code is still running in the background
2. right click and "open inspector in new window"
3. click in the Elements tab of the inspector and scroll up and down several times
4. click back onto the web page and try to scroll - if you reproduced it that page should look frozen, but you can see the status bar updating with links you hover over
5. resize the frozen window to make it start updating again

It's a little tricky to reproduce because sometimes the web view keeps updating fine, but the inspector freezes! Seems something weird is going on with the visibility or something of the views? Like one of then thinks it's hidden so doesn't draw updates.