I think... the spell went wrong.

About this image

So, I'm walking around Whiterun when all of the sudden, A Nobleman appears. I run up behind him and use a Psijic spell, "Shadowstep", and when I reappear... his horse had vanished! Well, I mean there's was still a vague image of the steed, but it still looked odd watching him float down the road. All I could do was sit and watch while I laughed for a good 3 minutes. 

I'm sure I'm not the only mage who's had a spell backfire