IE11 css for one particular class not showing in new tab
<p>I have this very weird IE11 behavior which occurs with some of our customers out of the blue. </p>

<p>We have a large table filled with several codes. Every code has its own (background) color assigned. Say the code is SOS, the css for its class is:</p>

<pre><code>.cellSOS {
    background-color: #ff1837;
    color: #ffffff;
    height: 18px;
}
</code></pre>

<p>The HTML for a td looks like this:   </p>

<pre><code> &lt;div class="cellSOS" onmouseover="anyAction()"&gt;&lt;p&gt;SOS&lt;/p&gt;&lt;/div&gt;
</code></pre>

<p>In this case there are +/- 120 different codes.</p>

<p>If I load the page in IE11 the (background) color for all codes are shown correctly. Now the problem: if open the same page in a new tab, all codes have a (background) color, except SOS. The same problem when the page is opened with window.open. </p>

<p>If I use the developer tool (F12) and examine the cells, all cellXXX elements have their style defined  (the same format as .cellSOS). But when I examine a cell containing SOS, the style is not there. </p>

<p>I tried moving the class within the css to another position to see if that gave another result, but still it was SOS without (background) color.</p>

<p>I compared the HTML for the page displayed correctly and the faulty page and they are both the same.</p>

<p>The problem occurs not with all our customers, but when it occurs it is always just one code that gives this problem and in that case it is always the same code, no matter where I define the style.</p>

<p>I also tested it in IE8 and there it shows fine. FireFox and Chrome also display correctly.</p>

<hr>

<p>Solved, sort of:</p>

<p>I have found the cause, but not an explanation.
The codes used are activities, used in a planning system. There are also users in this system. There was a user with the code Sos, and that caused the cell for activity SOS to display without a style.</p>

<p>Note: there is no connection whatsoever between the classes for activities and users.</p>

<p>Also a fun fact: if I change the user code to SOS (all uppercase, now it is exactly equal to the activity code) the problem does not occur.</p>