Fuel leak (Overflow)

For some reason the Bike leaks fuel wherever i stop even though the tank only 1/2 full (2-3 gal) max. the fuel leaks from the overflow:

Bought the bike used... 07 SuperDuke I think the tank was replaced...

- Is it possible wheelies/standard bouncing from riding around could cause this
- It seems to leak medium to large puddles of gas (See below)
- There no visible leaks of gas other then the overflow
- Is there different Gas cap options ? maybe its not sealing completely my only guess? Pls Advise

Enclosed images of the leak on my site

http://web.me.com/j2.10/Janak/KTM.html