Abbreviation followed by newline doesn't work

[michelf]

This should produce an <abbr> tag in Markdown Extra:

abbr  
next line

*[abbr]: Abbreviation

Edit/Clarification: there is a two-space newline that transforms into a <br> at the end of the first line.

[michelf]

Another similar case where abbreviations don't work.

W3C[^hey]

*[W3C]: World Wide Web Consortium

[^hey]: footnote trumps abbreviation