I think air getting into the fuel system is a possibility. When the lift pump isn't running the fuel will try to drain back to the tank. If there is an air leak anywhere it will do. The lift pump purges the system at key-on but as I found when I recently changed my fuel filter, it dosn't get all of it. My engine stalled once before running normally. With an ear close to the tank (rear seats lifted) I could hear the pump running and air bubling into the tank from the return line, until the purging was complete. So: this could be used as an indication that you have a leak in the system.
Air leaking in does not necessarily mean fuel will leak out. Couplings, especially quick release ones can act as non return valves.
I had a whole filters worth of air to listen to. About 10 seconds. A leak might be smaller and hard to detect, so the longer you can leave the car, the better, and get someone to key-on while you listen.