字符串值在MySQL数据库中累积空格

I have a webpage where admin users can edit the text on the page. But when they insert the text into the mysql database, it sometimes adds more and more white spaces before the acual content.
If you place your cursur before the first word on the page and spam backspace for a while, the whitespace in the database dissappears. But over time, the more you keep editing the page, more and more whitespaces are added again.

I did a lot of trouble shooting, but I just can't figure out what causes the whitespaces to be added. It does not always happen making it really difficult to troubleshoot.

Here's my code:

As my code is pretty long, I tried to translate most of the content to english.
If you want to translate something that in't already translated, the original language is Dutch.

over_ons.php - Shows edit button and page content from the database.

//Active page:
$pagina = 'over_ons'; ?>
<input type='hidden' id='pagina' value='<?php echo $pagina; ?>'> <!--Show active page to javascript--><?php
//Active user:
if(isset($_SESSION['correct_ingelogd']) and $_SESSION['functie']=='admin'){
$editor = $_SESSION['gebruikersnaam']; ?>
<input type='hidden' id='editor' value='<?php echo $editor; ?>'> <!--Show active user to javascript--><?php  
} ?>

<!--Editable DIV: -->
<div class='big_wrapper'><?php
        //Get eddited page content from the database
        $query=mysql_query("SELECT inhoud FROM paginas WHERE naam_pagina='" .$pagina. "'");
        while($inhoud_test=mysql_fetch_array($query)){
            $inhoud=$inhoud_test[0];
        }

    //Show Content
    ?><div id='editedText'><?php echo $inhoud; ?></p></div>

<!--Show edit button-->
<?php
if(isset($_SESSION['correct_ingelogd']) and $_SESSION['functie']=='admin')
{?>
    <div id='sidenote'>
        <input type='button' value='Bewerken' id='sent_data' class='button' />
        <div id="feedback" />
    </div>
<?php }

javascript.js - Sents page content to the php file sent_data.php:

//If the system is in edit mode and the user tries to leave the page,
//let the user know it is not so smart to leave yet.
$(window).bind('beforeunload', function(){
var value = $('#sent_data').attr('value'); //change the name of the edit button

if(value == 'Verstuur bewerkingen'){
    return 'Are you sure you want to leave the page? All unsaved edits will be lost!';
}
});

//Make content editable and send page content
$('#sent_data').click(function(){
    var value = $('#sent_data').attr('value'); //change the name of the edit button

    if(value == 'Bewerken'){
        $('#sent_data').attr('value', 'Verstuur bewerkingen');  //change the name of the edit button
        var $div=$('#editedText'), isEditable=$div.is('.editable'); //Make div editable
        $div.prop('contenteditable',!isEditable).toggleClass('editable')
        $('#feedback').html('<p class="opvallend">The content from<BR>this page is now<BR>editable.</p>');
    }else if(value == 'Verstuur bewerkingen'){
                var pagina = $('#pagina').val();
                var editor = $('#editor').val();
                var div_inhoud = $("#editedText").html();
                $.ajax({
                type: 'POST',
                url:  'sent_data.php',
                data: 'tekst=' +div_inhoud+ '&pagina=' +pagina+ '&editor=' +editor,
                success: function(data){
                Change the div back tot not editable, and change the button's name
                    $('#sent_data').attr('value', 'Bewerken');  //change the name of the edit button
                    var $div=$('#editedText'), isEditable=$div.is('.editable'); //Make div not editable
                    $div.prop('contenteditable',!isEditable).toggleClass('editable')

                //Tell the user if the edditing was succesfully
                    $('#feedback').html(data);
                    setTimeout(function(){
                        var value = $('#sent_data').attr('value'); //look up the name of the edit button
                        if(value == 'Bewerken'){ //Only if the button's name is 'bewerken', take away the help text
                        $('#feedback').text('');
                        }
                        }, 5000);
                    }
                    }).fail(function() {
                    //If there was an error, let the user know
                        $('#feedback').html('<p class="opvallend">There was an error.<BR>Your changes have<BR>not been saved.<BR>Please try again.</p>');
                    });
    }
});

And finally,
sent_data.php - Get page content from javascript,js and insert into database:

<?php
session_start();
include_once('./main.php');
include($main .'connectie.php');

//Look up which page has to be edited
$pagina=$_POST['pagina'];
//Get the name of the person who eddited the page
$editor=$_POST['editor'];
//Get content:
$tekst=$_POST['tekst'];
$tekst = mysql_real_escape_string($tekst);
$tekst = trim($tekst);

$query="UPDATE paginas SET naam_editer='" .$editor. "', inhoud='" .$tekst. "' WHERE naam_pagina='" .$pagina. "'";

}
    if(mysql_query($query)){
        echo "<p class='opvallend'>Successfully saves changes.</p>";
    }else{
        echo "<p class='opvallend'>Saving of changes failed.<BR>
        Please try again.</p>";
    }
?>

Extra information:
PHP version: 5.5.15
jQuery version: 1.11.1
Testing in browser: Chrome
Database: phpMyAdmin 5.5.39
The content is inserted in a VARCHAR type with space for 10000 caracters

Thanks in advance for you help!

SOLUTION

Thanks to the great help of a lot of people, and especially @avnishkgaur, it is working perfectly now. Here is what I ajusted (also changed it in my code above, so that's working code now).

1. Removed all the white spaces I had in my code between <div id='editable'> and <?php
2. Added $tekst = trim($tekst); to my PHP file to remove white spaces (didn't work)
3. Placed the editable text into another div as the code for getting the data from the database (was in the same div before)
4. Renamed the ID from the editable div to editedText. Also changed the name in the javascript file. This solution made it work perfectly (it was 'editable' before).

This was kind of an unexpected solution, so I think this could help others too.