Ethics of Sponsorship

What is the ethics of accepting a (sponsored) invitation to lecture, then doing a side hop? Here's what I discovered. One needs to "clock in" and "clock out" at the same place. Say one clocks in in Malta, as per sponsorship, then one clocks out in Malta. This is what I have done. That is, one retraces one's route. OBSERVATION: "Clocking in" and "clocking out" in Malta has however meant that I am at the moment undertaking one of my longest ever journeys by air -- if one includes transfers. It got complicated. My return journey may be close to 50 hours from start to finish. My longest was, I think, 60 hours.

POSTSCRIPT: Someone commented: some companies permit one to buy return tickets on the basis of fair use of funds, or equivalent use.