Bug overview description.
Very few wiki pages have a few HTML tags out of their place.

What part(s) of the site page(s) are affected?
Very few wiki pages.

What is the expected behavior?
The vast majority of wiki pages have a chunk of HTML akin to this:

<div id="content">
	<div id="wiki-show" class="wiki">
		<div id="sidebar">[...]</div>
		<h2 class="title">[...]</h2>
		<div id="wiki-body">
			<div style="margin-bottom: 1em;">[...]</div>
			<div style="margin-bottom: 1em;">[...]</div>
		</div>
		<div id="Clear">[...]</div>
	</div>
	<div id="Clear">[...]</div>
	<span style="width: 151px; font-size: 100%; display: block; float: none; margin: auto; position: static;">[...]</span>
</div>

What actual behavior is given instead?
In very few pages the HTML code is altered. Notice that the second <div style="margin-bottom: 1em;"> is "pushed" out of its container, taking the place of the <div id="Clear"> tag which is "pushed" out as well, as well as the second <div id="Clear">. The empty <span [...]> tag is deleted entirely. Visually, however, the only difference is that the text reading "Recent posts" is squeezed to the right of screen, instead of keeping to the left, as standard.

<div id="content">
	<div id="wiki-show" class="wiki">
		<div id="sidebar">[...]</div>
		<h2 class="title">[...]</h2>
		<div id="wiki-body">
			<div style="margin-bottom: 1em;">[...]</div>
		</div>
		<div style="margin-bottom: 1em;">[...]</div>
	</div>
	<div id="Clear">[...]</div>
</div>
<div id="Clear">[...]</div>

Time of incident (if applicable).
n/a

Can you reproduce the bug every time?
Yes.

What steps did you take to replicate this bug?
Simply visit one of the affected wiki pages. I've found two: cinderkiss and rossi_thukigata

Errors or other messages returned (if any).
n/a