Tidy replaces whitespace in HTML tags, so <li> foo </li> or <td> bar </td> renders as <li>foo</li> or <td>bar</td>. Separately, it also adds a newline after tags. So, <li>x</li><li>y</li> renders as <li>x</li>\n<li>y</li>. In most cases, this dual whitespace mangling behavior has no effect on rendering or display. However, in scenarios where there is a CSS rule that has an effect on whitespace (ex: white-space: nowrap or the ref [[https://en.wikipedia.org/wiki/MediaWiki:Common.css|hlist css rules in enwiki common.css]] that uses the display:inline property for list items), the stripped whitespace in tags OR the added newlines between tags becomes important). For any other tool that processes wikitext / HTML output without mangling whitespace, there can be rendering differences.
**Original bug description below**
When I go to edit just about any page invoking the .hlist CSS (ref [[https://en.wikipedia.org/wiki/MediaWiki:Common.css|common.css]]), I see a preview where any leading curved bracket has a space inserted after it (which is not present in the wikitext nor indicated by the css). [[https://en.wikipedia.org/wiki/Template:The_Legend_of_Zelda |Example template using sublists]].
I would expect this is a Parsoid delta. Firefox 50+ on Windows 7/10.