Thanks jib and ITA Hacker! Good to know!
To further clarify my first post (I just realised it wasn't very clear), I meant that I tried to enter a route from AAL to BLL into either ITA or TK's website with no results. I assume that meant that the route doesn't exist or that you're not allowed to stop at BLL, which was why I was puzzled by the 'stop' that appeared on ITA from AAL to IST.