Okay, so this is an interesting situation. I say this with some irony.

I finally decide to give the annoyingly oft-plugged client a try after considerable time resisting, and one of the first games I install, that being this, has no icon while the others are all there. I rather like seeing the unique icons in the list as that can be one thing to separate it from Steam.

So yeah, does anyone else have this issue or knows a way to fix it?

Well, for whatever reason, after DotT crashed and I had to restart my computer.. the icon was there after restarted GG so who knows what was going on. Sorry for the trouble.