We have 1,540 questions and some users started to retag them in big numbers. Therefor fresh questions get hidden and disappear from the front site, where old, answered questions pop up, and also closed questions.
And those questions reappear in the RSS feed. Unfortunately "New Questions" doesn't have its own feed. (Hint from @MusiKk)
Retag questions while they're new. The current situation is disturbing, while well meant.