I have seen what seems to be a defect, and it seems to be present in multiple browsers.
If I use Header 1 followed by Header 2, followed by Header 3, then everything appears well-formatted in the editor and sufficient space in between the headers. The same is true when I preview the page, but all the spaces are lost when I post the page.
This is in the editor
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This is the preview
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This is after posting
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Is there anything I can do to fix this on my end or is the a fix for the Atlassian developers?