Usually when I steal a ship it becomes mine as soon as I sit in the pilot seat and take off.Stealing ships has become my favourite activity! Whenever I see a ship land somewhere, I immediately drop what I am doing and head there. Sometimes multiple ships land in sequence (I mean not at starports) and I try to note where each one is.
Why?
Because
However I had one case where the ship took off while I was on board fighting with the crew. I entered the cockpit and killed the pilot, and then sat in the pilot seat. I was already in space. I had full control of the ship, but it wasn't actually mine, as I discovered when I landed and tried to sell it. It wasn't in my list of ships, even though I had just arrived in it and it was sitting right there.
I had to re-board it and sit in the pilot seat again, and suddenly I was the owner. I guess a bug?
I was quite surprised when the ship took off just after I had boarded it, though. Never had that happen before. I could have stowed away and maybe they would have taken me to their base or something.