Ref. definitions with same labels

[mity]

[foo]: /foo
[qnptgbh]: /qnptgbh
[abgbrwcv]: /abgbrwcv
[abgbrwcv]: /abgbrwcv2
[abgbrwcv]: /abgbrwcv3
[abgbrwcv]: /abgbrwcv4
[alqadfgn]: /alqadfgn

translates to

<p><a href="/foo">foo</a>
<a href="/qnptgbh">qnptgbh</a>
<a href="/abgbrwcv2">abgbrwcv</a>
<a href="/alqadfgn">alqadfgn</a>
[axgydtdu]</p>

I.e. MD4C now does not guarantee that first reference definition of the same label is used.