Did some debugging and found the bug.
In the file social-sharing-toolkit/includes/buttons/button.delicious.php
, the function signature is wrong:
function dl_delicious($url, $title, $type, $id, $text = '', $icon = '')
It’s missing two parameters, which causes the icon parameter to hold the description string instead.
Replacing the signature with the correct one below fixes the bug.
function dl_delicious($url, $title, $type, $id, $media = '', $description = '', $text = '', $icon = '')
Any hints about the upcoming release?