When I uncomment the alert the data is there... like:

{ 
      'Huishoudelijke hulp': 'Huishoudelijke hulp', 
      'Verpleging thuis': 'Verpleging thuis',
      'Verzorging thuis': 'Verzorging thuis',
      '24 uurs zorg': '24 uurs zorg',
      'Ondersteunende begeleiding': 'Ondersteunende begeleiding',
    }   

But instead of populating the key and the value it takes the whole var and start to create a key and value pair for each character.

You can see this in action here: http://www.zorgzuster-zeeland.nl/site/static/calendar_test.php

create a task in the calendar and then try to edit the task by clicking on it. It should populate the dropdown field properly.

When i create a static var with the same values the dropdown works.

static variable

var zvmlist = { 
      'Huishoudelijke hulp': 'Huishoudelijke hulp', 
      'Verpleging thuis': 'Verpleging thuis',
      'Verzorging thuis': 'Verzorging thuis',
      '24 uurs zorg': '24 uurs zorg',
      'Ondersteunende begeleiding': 'Ondersteunende begeleiding',
    }; 

This is my function, anybody has a clue?

$.get('get_zorgvormen.php', function(zvmlist) {
        //alert("Data Loaded: " + zvmlist);

            $.each(zvmlist, function(key, value) { 
              var selected='';
              if(key==eventdata.title){var selected='selected' }
              $('<option value="'+key+'" '+selected+'>'+value+'</option>').appendTo($('#calendar_edit_entry_form_title')); 

            }); 

        });