I make a large number of edits across Super User every week, but I've not seen this issue before.
If I try to make any edits to this answer, the text available for me to edit is trimmed short - only the very first part of the answer is shown, the rest seems to have disappeared.
Answer as shown originally

Answer as shown during editing

x" type question, I closed it as non-constructive. I left it undeleted though so the devs could check it out and figure out what's wrong with editing. – nhinkle♦ Nov 15 '11 at 6:25