When the line is emphasized and ends with some link-like text, the syntax // for emphasize at the end of line is considered as belonging to the link and the <em> tag isn't closed there, rendering this line and all following text incorrectly.
A working test case:
http://www.vrn123.ru/wiki/playground/wrong
=== Test page ===
//Some additional information you fill find at www.somesite.org//
Next paragraph
=== Output ===
<p>
<em>Some additional information you fill find at <a href="http://www.somesite.org//" class="urlextern" title="http://www.somesite.org//" rel="nofollow">www.somesite.org//</a>
Next paragraph
</em></p>
=== Expected output ===
<p>
<em>Some additional information you fill find at <a href="http://www.somesite.org" class="urlextern" title="http://www.somesite.org" rel="nofollow">www.somesite.org</a></em>
</p>
<p>
Next paragraph
</p>