While my WoW character is in combat and I have SilverDragon addon (tested this by turning off ALL other addons), I get an error in chat saying "Interface action failed because of an AddOn" (and NO lua error window, just this yellow text in chat) when I try doing one of those things:

• try to open tracked achievement (sometimes works, sometimes not)
• try to open tracked quest (sometimes works, sometimes bugs)
• try a new armor piece in dressing room (not equip) (sometimes works, sometimes bugs)
• try to open a quest from tracked quests (sometimes works, sometimes bugs)
• open dungeon journey ("Adventure guide") and click on a boss (always bugs)

Edit:
To reproduce: turn off all addons except SilverDragon, go to a training dummy, attack it, then open a world map, go to Pandaria and click on world boss like Sha. Bugs every single time.

Anyway, I can't reproduce this. (Or, rather, I do currently have a tainted UI, but disabling SilverDragon doesn't change that... and taintlog doesn't attribute anything to SilverDragon.) Lacking more information, closing this.

Is that only after you've met a rare, or always?

I am very sorry for not responding earlier, had a break from WoW.
I came back now, updated addons (it was weird that WoWUp didn't recognize the addon anymore) and yes, I still do have this problem :(
You can easily reproduce it by turning off all addons except SilverDragon, going to a training dummy, attacking it, then opening a world map, going to Pandaria and clicking on world boss like Sha. Bugs every single time.

Can You please reopen the issue? Or do I have to register it again?