Unicorn PTC fuse possibly a bad design?

I was just playing with my Junebug and having it connect to chips and stuff so when I plugged in my Unicorn into the USB port (it had no programming, just to power it) the LED did not light up (I added a power LED). I then short out the PTC fuse and it powers up. I then de-solder the PTC fuse and take off the plastic cover and look inside at the spring? thing and I see that it is fried! I never powered from the USB before so I am wondering whats up. I replaced it with a ferrite bead.

It's a fuse, the thermal fuses were too high a resistance. I've stopped using them (the fuses) and now the kits come with a ferrite bead as your USB port is current limited and self resetting. That's a 1.2A fuse, kinda hard to blow. How did you manage to short out the Unicorn?

Edit, a ferrite bead is the right thing to put there

PS Bad design I hope not. Works great for me.