Extremely annoying!
I thought first that it is related to the guild store add-on I use (Awesome Guild Store), but found only comments regarding other types of errors. I find it strange that I can see only the above two posts on this topic, which makes me think that the majority do not experience this problem... Do you use any kind of guild store add-on at all?
Anyway, I will try to disable the add-on when playing next and see.