We've noticed a bug with Internet Explorer 11 which causes users to not be able to delete their contacts from their Plus panel and also causes a problem with deleting files from your transfer overview. When you choose to delete a file, it will not be removed from the transfer overview but if you close the panel and open it again, it will be gone! This means files can be deleted albeit in a clunky manner and contacts cannot be deleted at all I am afraid.
If you need the contacts deleted ASAP, downloading another browser in the meantime will act as a workaround for now.
We are currently looking into this issue, thanks for your patience.