Vaughan Pratt, the bug you’re talking about is one which has been discussed, and diagnosed, here on this blog before. The problem is HTML allows you to include extra characters in certain flags without changing their functionality. WordPress was coded without this in mind, and that’s where the problem crops up.
Normally WordPress knows to close tags which weren’t closed properly, but WordPress does a string match for the exact flag people normally use. If you include extra characters in the tag, WordPress won’t recognize it, and thus, it won’t know to close it. That means the tag will be parsed by HTML like normal, and it will be considered open. Since WordPress doesn’t close it, it continues for the rest of the page. Even worse, WordPress won’t allow you to post a closing tag in a separate post as it will think it’s unmatched and strip it.
(I believe there are just two characters that can immediately follow the “i” in the tag and cause this bug are the space and forward slash, but I might be wrong. Not that it should matter, but you can actually then follow the extra character with any character you want, as many times as you want.)