Replying to Two People Logged In One Name

I was on the site the other day and noticed that over in the quick chat, someone else was talking under my name. They were also confused and didn't know what happened. We were both logged under my name for some reason. He had logged under his name, but came in under mine. He logged out, and so did I. We both then logged back in and everything was fine. Do you know why it happened or how it can be prevented? thanks!!!
---Sex is like playing cards, if you don't have a good partner then you better have a good hand!---