According to point 5.3 of the CommonMark specification, the number of the first item in an ordered list should be used as the start number for this list:

The start number of an ordered list is determined by the list number of its initial list item. The numbers of subsequent list items are disregarded.

So, the code

2. second
3. third

should be rendered as:

<ol start="2">
<li>second</li>
<li>third</li>
</ol>

In XWiki, however, it is rendered as:

<ol>
<li>second</li>
<li>third</li>
</ol>  

This means that the list starts with 1. when it should start with 2.

This problem appears regardless of whether the list marker has the form 2. or 2).