I've never seen this happen before and I can't find a report on it. If it's known then sorry for wasting your time. =)
It happened on the custom track "Forgotten" by InF1ictor

Here's exactly what I did and the ensuing bug.:

I did not view any replays before playing.
I played the track once with the Phoenix.
I then played it with the Scorpion but didn't complete it.
I then viewed the #1 replay (A Bipolar Behr).
I then replayed the track twice with the Phoenix.
I viewed the same replay, and found that it had been replaced by a replay of myself, tooling around on the Scorpion. It was not a replay of my actual run with the Scorpion, just puttering about.
Also, my rider was wearing the pants I had on yesterday, not the ones I had on when riding the track had never been on that track before). This may not be significant, but who knows...bugs are weird.

edit: I just got back into the game and checked it again. It's back the way it should be, so I guess it just messed up the replay for me, not universally or permanently.