Interesting. A few years ago I had to go down to STT for business, but had a previous commitment one night that I had to fly back for in the middle of the trip, and fly back to STT the next day to complete the work. Booked the first out, and final back as one trip. Then booked the "middle" back and out part as a separate trip.

start of trip: MCO > STT middle: STT > MCO > STT return: STT to MCO

Now this was on American, but they didn't give me any grief about it.