my 03 speedie is fine but had a similer problem with an older ford falcon car. It turns out that the discs on the front (why only the front I dont know)of the car were warping when leaving the brake on while stopped. the heat in the pads were heating up one section of the rotor over time this disimiler heat on the rotor caused warping.the cure using the hand (park) brake when stopped foot off the brake pedel
dont know if this is happening on the bikes or not it was just a thought.(use footbrake while stopped rather than front brake might help?)
