The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.
The WebBrowser is a WinForms/Native control wrapped in WPF shell and there may be the "wpf airspace problem" meaning that no wpf pixel can be rendered over a winforms pixel. The compasses consist of wpf pixels, because they are drawn in the adorner layer, I think. This should not be solveable in this case.