Have confirmed via a reddit thread that I am not alone in seeing this.
Pretty much every ability in every class is missing its icon, in what seems to only be the skill calculator. I can click an individual skill and go to its own page and the icon will be displayed, but not in the skill calculator at all. Makes putting a build together a little weird.
This has only been an issue over the past two months or so. It started with a few skills at first, one random grey square here and there, but now its evolved to be about 90% of them.
edit:
http://i.imgur.com/mwqaBEp.jpg (picture of the problem)