A man named Dan.
A big ball of Wibbly-Wobbly, Timey-Wimey _stuff_
Spoiler, Left/Center/Right, and Youtube tags are broken.
Font size tags (e.g. Small, Normal) require two newlines to keep them on separate lines. Font style tags (e.g. bold, italic) only require one. This behavior should be consistent between all tags.
See this post.
Developer, administrator, and style wrangler