Yes, a similar problem exists on other broken sites with fixed position headers and/or footers. I hit space, then scroll up a bit to find where I am up to. Atlassian’s Jira is a huge offender and I have to use that at work every day.
I think the browsers are complicit in that particular example of user hostility, but I’m not sure there’s any good solution for them to implement. The browser would need to somehow detect how big the viewport really is and scroll just that far, but sometimes the scrolling itself means the fixed position overlays move around.
I think the answer is site designers need to be aware of it and just not cover part of their content with irrelevant stuff. And make sure all of the content, or at least “enough” content, is loaded so the browser can do the right thing. That was totally a dig at infinite scrolling, just for you.
Both fixed position headers and footers and Discourse’s infinite scrolling are abuses of the browser’s idea of what a page is, and it’s not surprising that problems result from it. I really like the concept of not having to hit “Next page”, just keep scrolling for more content, but I don’t know how you can display a not-a-page like that in a browser of web pages without problems.