When answering this question, I wanted to simulate the comment limitation that you can't have bold italics, as it renders as ***only bold*** on comments, but I realized that on the HTML preview it renders as **only italics**, while on the question itself it renders correctly.
This seems to invert both cases.
Of course, this is quite an edge case, not many will go around using
\***only bold**\* or
**\*only italics\***, but I can imagine cases where this would be a problem.
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