I was having trouble saving my last post (back when I was using WordPress), apparently because it contained the following content:
When you paste that into a new post and click preview, it actually shows a
preview for the previous post! After returning to the posts list, I’m not even
able to edit it again, it triggers a 404. But the content made it to the
database OK: I was able to verify it with mysql on the command line.
Various substrings do not trigger the erroneous behavior.
I don’t know what the heck is going on. I tried greping around in the
WordPress source code, but wasn’t able to find anything that looked like it was
treating that text as a special case.