Effects accidentally recorded to audio track

I’ve being using Cubase Studio 5 since its release, and yesterday I was once again recording vocals.
But listening back to the tracks today, I was surprised to find that a reverb effect had been added to the audio tracks themselves.
As I understand (correct me if I’m wrong) the default setting for Cubase is to record without effects. Furthermore, there weren’t any effects activated on the track I was recording on: It was routed to a group track where a bit of reverb was applied. Can this be the reverb that was applied to my track? And what can I have done wrong - and how can I avoid this issue in the future?
Thanks in advance.