Unbalanced flex wrapping

HTML

<nav>
  <ul>
    <li class="here"><a href="/">Home</a></li>
    <li class=""><a href="/research/">Research</a></li>
    <li class=""><a href="/publications/">Publications</a></li>
    <li class=""><a href="/protocols/">Protocols</a></li>
    <li class=""><a href="/people/">People</a></li>
    <li class=""><a href="/contact/">Contact</a></li>
    <li class=""><a href="/help/">Help</a></li>
  </ul>
</nav>

CSS

nav {
  border-radius: 1ex;
  font-family: sans-serif;
  overflow: hidden;
}

nav ul {
  display: flex;
  flex-wrap: wrap;
  margin: 0;
  padding: 0;
}

nav li {
  display: inline-block;
  flex-grow: 1;
  text-align: center;
  border-top: solid white 1px;
  margin: 0;
}

nav {
  background: #ff9c3f;
}

nav ul a {
  display: block;
  color: white;
  text-decoration: none;
  padding: 0.5ex 8px;
  text-shadow: rgba(0, 0, 0, 0.75) 0px 0px 2px;
}

nav .here>a {
  background: #8f0000;
}