Looks like theme_advanced_fonts has problem and not fixed yet.
I'm using an alternative solution with style_formats to define fonts
tinymce.init({
...
toolbar: "styleselect",
style_formats: [
{title: 'Open Sans', inline: 'span', styles: { 'font-family':'Open Sans'}},
{title: 'Arial', inline: 'span', styles: { 'font-family':'arial'}},
{title: 'Book Antiqua', inline: 'span', styles: { 'font-family':'book antiqua'}},
{title: 'Comic Sans MS', inline: 'span', styles: { 'font-family':'comic sans ms,sans-serif'}},
{title: 'Courier New', inline: 'span', styles: { 'font-family':'courier new,courier'}},
{title: 'Georgia', inline: 'span', styles: { 'font-family':'georgia,palatino'}},
{title: 'Helvetica', inline: 'span', styles: { 'font-family':'helvetica'}},
{title: 'Impact', inline: 'span', styles: { 'font-family':'impact,chicago'}},
{title: 'Symbol', inline: 'span', styles: { 'font-family':'symbol'}},
{title: 'Tahoma', inline: 'span', styles: { 'font-family':'tahoma'}},
{title: 'Terminal', inline: 'span', styles: { 'font-family':'terminal,monaco'}},
{title: 'Times New Roman', inline: 'span', styles: { 'font-family':'times new roman,times'}},
{title: 'Verdana', inline: 'span', styles: { 'font-family':'Verdana'}}
],
...
});
result: