Not sure if this has been reported before, but I had a game where I got multiple mission turns in row due to fleet (presumably). I had bought fleet and emptied provinces while buying mission, so I get a mission turn and a fleet turn. However, on that mission turn, I decided to buy mission, and the UI gave me a second mission turn before the fleet turn. I continued to buy mission every turn, and it kept giving me mission turns until I stopped buying mission and then it gave me my fleet turn before ending the game. Game ID 166125973.
Thanks for the report, that is something I have not heard before. It clearly is a bug.