Wikitext like
<li>Foo <li>Bar
Renders as <ul><li>Foo</li><li>Bar</li></ul> in the PHP parser (the unclosed <li>s are closed, and the newlines are swallowed), but Parsoid renders it as:
<li id="mwAQ">Foo <p id="mwAg"><br id="mwAw"></p> <p id="mwBA"><br id="mwBQ"></p></li> <li id="mwBg">Bar</li>
Apparently template authors expect this newline swallowing behavior and rely on it, see T100921#1354936.