If the rendering changes / breaks when the skin is switched, it is very likely a CSS difference. In any case, it is nothing related to Parsoid since you are looking at output of the core parser.

Minerva doesn't touch HTML so any margins are likely controlled by CSS and visual differences with different skins is to be expected

How does this impact end users?

@Jdlrobson see below, the indentations after the first item are wrong

We're expecting the output under II to be:

But instead it is generating as:

Notice the lack of a <dl> generation

And this only appears to be off in minerva

Okay you shared the link to desktop Minerva, not mobile, and I can only see the invalid HTML only when adding the mobile domain e.g.:
https://test.m.wikipedia.org/w/index.php?title=User:Xaosflux/sandbox&oldid=464254&safemode=1&useskin=minerva

The MobileFormatter in MobileFrontend can trip up when given invalid HTML. That results in the visual difference.

The parser is generating invalid HTML
https://validator.w3.org/nu/?doc=https%3A%2F%2Ftest.wikipedia.org%2Fw%2Findex.php%3Ftitle%3DUser%3AXaosflux%2Fsandbox%26oldid%3D464254%26safemode%3D1%26useskin%3Dfallback

@ssastry this is either a bug with the parser or a case of garbage in garbage out. I'll let you decide:

Specifically

<div><ol style="list-style-type:upper-roman"><li>''Aaaaa''
:AAA.</li><li>''Baaaa''
:BBB</li><li>''Caaaa''
:CCC</li><li>''Daaaa''
:DDD</li></ol></div>

Is outputting as

<ol style="list-style-type:upper-roman">
    <li>
        <i>Aaaaa</i>
        <dl><dd>AAA.</dd></dl>
    </li>
    <li>
        <i>Baaaa</i>
        <dd>BBB</dd> <!-- invalid HTML here-->
    </li>
    <li>
        <i>Caaaa</i>
        <dd>CCC</dd> <!-- invalid HTML here-->
    </li>
    <li>
        <i>Daaaa</i>
        <dd>DDD</dd></li> <!-- invalid HTML here-->
</ol>