Last modified: 2011-04-14 15:14:19 UTC
These should be symmetrical, but they are not. When deleting whitespace, the software collapses it and does not show it as a change.
You may need to add
border-bottom: 1px solid #f00;
to your CSS to see the difference properly.
CC'ing Nikerabbit, who added the class.
I have no idea what has happened, there is no such class in example urls anymore.