I was just trying to clean up Understanding why $\pi_{3}(N) = \mathbb{Z}_{(2n, n^2)}$? , which was originally almost entirely cut-and-pasted images without any alternate text. For the first image, I gave it the alternate text:
Arkowitz and Golasinski - Co-$H$ structures on Moore spaces of type $(G, 2)$, p. 673
This worked fine in the preview, but, when I posted the change, everything after the first dollar sign (including the trailing />
of whatever HTML is generated by the Markdown processor) had escaped into the text of the post. Since my instinct was to leave a clean post, I fixed it (removed the dollar signs) and didn't get a screen shot, so I'm afraid I can't document beyond just this description of what happened. (Because I did it within the grace period, I think that the original error won't even show up in the revision history; and it seems that editing again just to artificially re-insert, and then fix, the error would not be appropriate.)
Why does the preview handle this correctly, but not the main post?