I too blew [aka melted] a fuse on a unit which had been running perfectly for 3 months. I had disassembled it to take the new HD pictures and put it back together. The fuse melted within a few hours, but the unit was absolutely fine with a replacement. Could have been static, could have been bad placement of the fuse (doubtful), who knows. What we do know is the fuse is pretty close to the max power of the fuse.
Its also nothing to do with fans, the Cube has PWM detection and will stop hashing if the fan fails. You can test this yourself (please dont).
I think the important part is: "disassembled it to take the new HD pictures and put it back together". That means that the fuse probably did not have a good connection when it was replaced and overheated due to a poor fuse/connector connection. By replacing the fuse the next fuse had a better connection and survived.