While looking at Ringpull I discovered an Internet Explorer 6.0 bug that can affect E2 writeups. This bug can be reproduced outside of E2, so it's not an E2 code issue.
Something about the following block of HTML makes a paragraph that comes after it immune to normal HTML line breaking, and it just continues endlessly to the right, finally moving out of the display frame entirely. It seems that the PRE tag is still partially (but not fully) in effect.
<pre>
<br /></pre>
A demonstration (for IE users, obviously)
TEST
Internet Explorer bug: Something about the preceding block of HTML makes this paragraph immune to normal HTML line breaking, and it just continues endlessly to the right, finally moving out of the display frame entirely.
It seems that the PRE tag is still partially (but not fully) in effect.
Lesson: Don't use <br> tags inside a <pre> block.