It's a Blizard UI bug. It also causes issues with raid markers.

Happens all the time with.. DBM, Vuhdo, recount, *insert addon here*:

Here's the reply about it from the Vuhdo developer:

"Both errors you're reporting are actually blizzard bugs. It is not vuhdo alone that triggers them. If you turn vuhdo off and play for a while, you're going to find a number of other addons that will "trigger it". But those bugs in fact appear even with all the addons turned off. Glyph UI in particular is notorious for appearing with or without addons, but if you're running with addons, it will just tack on the error on whatever addon. But vuhdo doesn't really have anything to do with glyphs nor does it touch the glyph pane in any way.
In short, until blizz decides to fix their code, there's nothing to be done but hit /reload ui."

I used SilverDragon up until it wasn't being as reliable and having issues in Cata. I have since switched to NPCScan. The only problem with the latter is it will register hunter pets as the named mob, so then cache it, and the cache will need to be dumped. SD didn't do that.

Actually, there is a mod that mitigates the Blizzard UI error:
http://www.wowace.com/addons/inspectfix/

Probably a good one to mention in the next Addon Spotlight, since it is super useful and it seems few people are aware of it.