What usually happens in this situation?

I usually stick to 20xx leagues but had a credit to burn and used it on a 90's mystery league just to try it out. Autodraft occurred today and I noticed that the same owner has two teams in the league. If one of the teams is removed by Strat-O-Matic, is there a redraft or can someone volunteer to take over the already drafted team? Really unusual that someone would attempt to put two teams in the same league. Never saw it before.

It _is_ actually allowed. When you setup a league there is a non-default option to allow a single "owner" to have more than one team in the league. A legitimate example of this I've seen used is when someone, say, lets their son play a team. Don't always assume the worst.

If SOM does intervene, they assign a different owner and the draft stays like it is. I've seen them do this too when someone joins a league with (obvious) bad intent.

For this league I would privately inquire of the person with 2 teams what is up. If the explanation is reasonable then let it slide. I encourage you not to make an accusation of wrong doing until the person's actions call for it. As apolivka says there may be a legitimate explanation.

If you are uncomfortable with possibility of someone having 2 teams in a league then be careful in the future to check the settings for a league before you join.

It was the same guy with two teams in the league. He said it was an accident although he never responded to any of our requests for clarification until Strat stepped in and took over one of his teams. Then he said it was just an accident. One of the teams he drafted the best 2b and SS in the set and the other team he drafted the top SP's in the set so not sure how much of an accident but its resolved anyway.