Special chars ignored in abbreviations

[Dave Newton]

Some characters get ignored in abbreviations.

Input:

*[µg]: micrograms
*[g]: grams

* µg
* g

Expected output (and output from PHP Markdown Extra):

<ul>
<li><abbr title="micrograms">µg</abbr></li>
<li><abbr title="grams">g</abbr></li>
</ul>

Actual output:

<ul>
<li>µ<abbr title="grams">g</abbr></li>
<li><abbr title="grams">g</abbr></li>
</ul>