flexslider vs featured image vs second image

i inserted a new/second image on top into a service-posttype that already had a featured image set. I expected this new images to override the featured image locally/on page display. but what happened was, that the new image appeared along with the featured image in a flexslider (that surprisingly appeared). And the new image was shown a second time just below the flexslider.

So i deleted the second image, but for miracle reasons it stays in the non editable flexslider. It keeps showing on page display in the felxslider, although i deleted is. I cannot edit the flexslider since it doesnt show up/is hidden in de page-editor.

is this a bug?

see http://nieuw.kreanova.nl/services_item/brainstorm-begeleiding/