Strange bug in Chrome under Linux. Bug or layout problem?

Question

css

Should be :
Bug :

Block with phones in the header periodically slides down for some unknown reason. If you refresh the page , it returns to its proper place in the upper right corner.
After a while - it is enough just to click on the menu items - it slides down again.
Now the header code is:

<header class="header">
  <div class="headerlogo">
    <a href="/"><img src="/img/logo-img.png"></a>
    <div class="custom_header">
      <h3>Наши телефоны:</h3>
      <p><a href="tel:[phone]">[phone]</a></p>
      <p><a href="tel:[phone]">[phone]</a></p></div>
    </div>
  </div>
  <ul class="menu_header">
    <li class="item-198"><a href="/about.html">О компании</a></li>
    ...
  </ul>
</header>

.header {
  margin-bottom: 1em;
}
.headerlogo {
  height: 154px;
}
.custom_header {
  margin: 1em .2em 0 0;
  text-align: center;
  float: right;
  padding: 1em;
  border: 1px solid #ccc;
  border-radius: 3px;
  box-shadow: inset 0px 0px 15px #eee;
}
.custom_header p {
  margin-bottom: .5em;
}
.menu_header {
  margin-bottom: 2em;
  border-top: 1px solid rgb(65,105,225);
  border-bottom: 1px solid rgb(65,105,225);
  padding: .1em 0 .2em 0;
  font-size: 1.1em;
}

You can see it here: is.sigmamedia.ru
There is no such problem in Mozilla, I haven't tested other browsers yet.

Answer 1

DIV drag a bit higher:

<header class="header">
  <div class="headerlogo">
    <div class="custom_header">...</div>
    <a href="/"><img src="/img/logo-img.png"></a>
  </div>
</header>

and for the logo, set the bounding parameters, height, width, etc.