Alerted value of the select inside the jQuery change function and saw it added a '\' to the end of the string. So, e.g., InfoJobs appeared as InfoJobs\
Solution:
var fonte = $("#fontes").val();
var fonteNew = fonte.replace("\\","");
Then, inside $.ajax
:
type: "GET",
and
data: {fonte: fonteNew},
In the PHP file, changed from POST to GET.