Apple Developer website scrolls badly, freezes, takes over other tabs in OW6

OmniWeb 6.0 v626 r238077, Yosemite 10.10.4 (14E46)

The Apple Developer website uses floating headers of some kind on the individual class reference pages, such as

After a certain (unpredictable) amount of navigation on the page, the scrolling doesn’t move the content, just the header. It seems to be related to the amount of time since the last scroll action. Additionally, the links no longer respond to clicks.

Once this has happened, reloading the page sometimes restores scrolling, although the problem will reoccur. If a reload doesn’t fix it, the contents of the page are displayed on the other tabs in the window, and this is not corrected by trying to reload those tabs.

And the application usually crashes when finally closing the window.

I’m trying to collect more certain data so that I can file a proper bug report, but I figured I’d publish this so far (it’s been driving me crazy today) in case anyone else has seen this and has a recommendation for me.

Similar scrolling weirdness seems to be happening here on the Discourse forum, likewise disabling links and causing crashes when the window is closed…

A screenshot of this at