Here's a possibility. Once the truck was hooked up, when retracting the landing gear, the switch stuck. With the noise of the running truck, talking or whatever may have been going on, the gear reached it's upper limit blowing the fuse. Some sort of limit switch would be great but blowing the fuse or popping a breaker is way better than busting a gear reduction unit. If your rig has an inline fuse for the legs, there is a circuit breaker type plug in fuse available.
The design of the landing gear nor it's capacity isn't really flawed in my opinion. Any time we hook the truck to the pin, we put pressure against that pin. Weather it's forward or reverse pressure, it's usually there. We then operate the landing gear with that additional pressure on the pin. Consider how often we pull into a site and raise the trailer to unhook and have to back the truck up a teensy bit more to releive the pressure against the pin so the hitch will release. There ya have it, we were just adding extra weight/pressure to the pin without knowing it while we were extending the legs.