The behavior of line breaks when it comes to magic links, like RFC or PMID, is different from the usual behavior of line breaks in wiki syntax. If there are more than two linebreaks between the lines, they will be put on different lines. However, if they are magic links, then they will still stay magic links, even with line breaks in between. That's quite unlikely the intention, and I would probably suggest to only allow regular spaces as separators of the "RFC"/"PMID" strings and the numbers. See http://test.wikipedia.org/wiki/Magic_links for some examples I've given.