DatePicker not showing properly on a modal window in Bootstrap 3 (Safari/Chrome)

I’m using AdminLTE/Bootstrap for a backend dashboard and I’m having a problem when showing modal windows with the DatePickers on it.

I have the following JS code to load content from other pages on it (I just add the class load-external to links):

$('.load-external').click(function(ev) {
    var href = $(this).attr('href');
    $('#externalModal').find('.modal-body').load(href);
    $('#externalModal').find('.modal-title').text($(this).attr('data-confirm-title'));
    $('#externalModal').modal({show:true});
    return false;
});

The problem is when in the div I load a form with a DatePicker such as:

<input id="agreement_payment_estimatedPayingDate" name="agreement_payment[estimatedPayingDate]" required="required" data-provide="datepicker" data-date-format="yyyy-mm-dd" class="form-control" value="2016-06-22" type="date">

the DatePicker is displayed below the modal window

In firefox it works properly but not in Chrome neither Safari.

Any idea why this could be happening?