workaround UploadField iframe incorrect height - https://github.com/silverstripe/silverstripe-framework/issues/2862

config.yml

LeftAndMain:
  extra_requirements_javascript:
    - mysite/javascript/fixUploadField.js

fixUploadField.js

(function($) {
	$.entwine('ss', function($) {
		$( 'div.ss-uploadfield-item-editform.opened').entwine({
			onmatch: function(e) {
				var self = this,
					editform = self.closest('.ss-uploadfield-item').find('.ss-uploadfield-item-editform'),
					itemInfo = editform.prev('.ss-uploadfield-item-info'),
					iframe = editform.find('iframe');
				iframe.on('load', function () {
					if (editform.hasClass('opened')) {
						editform.fitHeight();
					}
				});
				this._super();
			}
		});
	});
}(jQuery));