Class does exist but is not found

I am absolutely baffled bu this. Here's my CSS:

        $(window).load(function(){

           $('.zichtbaar').removeClass('zichtbaar').addClass('verborgen');

           $('#zoekitem').focus();



           $('.letter').on('click', function(){

               $('.zichtbaar').addClass('verborgen').removeClass('zichtbaar');

               var letter = $(this).text();

               var klasse = "LETTER-" + letter;

               var el = $('.' + klasse);
               
               alert(klasse + " - " + el.length);
               
               $('#alfabet-header').html(letter);

               el.addClass('zichtbaar').removeClass('verborgen');

           });

        });

        #zoekitem{

         font-size: 1.3em;

        }


        #letter-header{

         height: 32px;

         color: royalblue;

         font-size: 1.5em;

         font-weight: bold;

         overflow: hidden;

        }


        .letter{

         float: left;

         width: 3.7037037037037%;

         cursor: pointer;

         text-align: center;

        }


        #alfabet-header{

         font-size: 5em;

         font-weight: bold;

        }


        .inhoud{

         margin-left: 10%;

        }

        .verborgen{

         display:none;

        }


        #zoek-header{

         font-size: 2em;

        }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>
<div id="letter-header">
           <div class="letter">A</div>

           <div class="letter">B</div>

           <div class="letter">C</div>

           <div class="letter">D</div>

           <div class="letter">E</div>

           <div class="letter">F</div>

           <div class="letter">G</div>

           <div class="letter">H</div>

           <div class="letter">I</div>

           <div class="letter">J</div>

           <div class="letter">K</div>

           <div class="letter">L</div>

           <div class="letter">M</div>

           <div class="letter">N</div>

           <div class="letter">O</div>

           <div class="letter">P</div>

           <div class="letter">Q</div>

           <div class="letter">R</div>

           <div class="letter">S</div>

           <div class="letter">T</div>

           <div class="letter">U</div>

           <div class="letter">V</div>

           <div class="letter">W</div>

           <div class="letter">X</div>

           <div class="letter">Y</div>

           <div class="letter">Z</div>

           <div class="letter">0-9</div>

        </div>

        <br/>


        <div>

           <div id="alfabet-header"></div>

           <div id="zoek-header" class="verborgen">Zoekresultaten voor:</div>

           <div class="inhoud LETTER-A verborgen"><a href="www.appels.com" target="_blank">Appels</a></div>

           <div class="inhoud LETTER-B verborgen"><a href="www.boerenkool.com" target="_blank">Boerenkool</a></div>

           <div class="inhoud LETTER-B verborgen"><a href="www.bonen.com" target="_blank">Bonen</a></div>

           <div class="inhoud LETTER-B verborgen"><a href="www.bosbessen.com" target="_blank">Bosbessen</a></div>

           <div class="inhoud LETTER-C verborgen"><a href="www.citrus.com" target="_blank">Citrus</a></div>

           <div class="inhoud LETTER-K verborgen"><a href="www.kappertjes.com" target="_blank">Kappertjes</a></div>

           <div class="inhoud LETTER-T verborgen"><a href="www.tuinbonen.com" target="_blank">Tuinbonen</a></div>

           <div class="inhoud LETTER-W verborgen"><a href="www.wittekool.com" target="_blank">Witte kool</a></div>

        </div>

When I click A, B, or T everything is fine; The alert shows the number of elements that have the classname that I'm looking for and displays them. But when I click C, K or W, the elements, although they clearly exist, are not found.

I haven't got the palest shade of a clue as to why this happens.

Solution

You've got a lot of Unicode zero-width space characters in your HTML source, and in particular there's one at the beginning of the text for the "C" box. When you access the .text() of the element, therefore, it's not just "C".