tye gave the technical reasons why that /doesn't/ work, and did a good job, but he rather skimmed over the logical reasons why it /shouldn't/ work.

Logicaly, readmore isn't an empty tag that has an effect at a single place in your XHTML. Instead, it's a block-level (?) tag, which has an opening and a closing, and hides it's interior unless you're looking directly at the node (IE it's the root node of the page you're looking at). For convience, we allow you to ommit the close tag, in which case it's taken to be at the end of your node.

The empty-tag form in XML (that is <tag />) is defined to be a shortcut for opening, and then immedatly closing again (<tag></tag>). Thus, it logicaly should hide nothing, that is, do nothing.

(Of course, this doesn't explain why things /are/ they way they are, it mearly explains why they should be the way they are. tye's explanition is, as usual, correct, I just wanted to give another viewpoint, and explain why this isn't mearly a WONTFIX bug, but not really a bug at all.)