Sidebar in the post jumps to the top of the page

Expected behavior

The sidebar in the post should remain fixed on the right, visible to the user.

Actual behavior

If you open a post with a sidebar that is higher than the window (you must scroll to see full content), it may disappear / jump to the top of the page while scrolling up within the post.

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How to reproduce

Open a post in staging.busy.org (https://staging.busy.org/@justyy/utopian-chrome-extension-v0-0-9-integrate-stats-api-add-node-list)
Make sure that the sidebar does not fit the window (You can resize the window)
Scroll down to toggle the comment section so that there is enough space to scroll up
Scroll up / Scroll down

Browser: Google Chrome 64.0.3282.140
Operating system: Windows 10

Additional recordings

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Posted on Utopian.io - Rewarding Open Source Contributors