I tried searching all over the place to find this and couldn't, so if this is located somewhere else, I'm totally sorry. :x Also, sorry if this is miscategorized. I just installed the newest build of Auctioneer Suite because my Northrend stuff wasn't showing vendor information. No big deal and now it DOES show vendor information *thumbs up* However, I soon realized a problem.
The coin display was weird, as though transparency on the coin images was faulty. I run the client with my UI scale at the lowest possible setting and always have. This has not been an issue in the past. The graphical glitch doesn't occur when I have my UI scaled higher, but then I can't actually SEE the game because my actionbars are gigantic.
:( I was hoping maybe there would be some way around it, like I said, this wasn't an issue in the last version. But I see what you're saying about {circle}, it's all rigid and blocky, not at all rounded in a low-scale UI.
It is problem with Blizzard rendering engine. Try, for example, sending {circle} into chat. It will all be surrounded by colored dust. :(
I have the issue the OP has except it seems limited to only certain addons. Informant is one of them, Hitsmode was the other one. If I send {circle} into chat, I have no problems with the artifacting or "colored dust" even though my chat frame used the same font Hitsmode was using. I also have no artifacting on the font when it is instead displayed by Rating Buster which is using the same font for me as Informant is using.
I spammed myself with the raid icons to show I have no issue with their display while having a tooltip showing to show that Carbonite and Informant seem to have issues while Rating Buster, using the same font at the same scaling does not.