Possible Clutch Problem

Had an engine rebuild last winter which included a gearbox repair. It was done by a reputable engine builder/tuner who would ring me up if he found anything that he thought should be replaced while he had the engine in bits. The clutch was thought to be OK.
Recently rode to the Isle of Wight and back (400 miles) with absolutely no problems. Due to holidays, the scooter has been stored in the garage since. Last night I started it up to go to a club meet and when I put it in gear it lurched forward and stalled, even with the clutch pulled in. After 3 or 4 times of doing this it settled down and behaved "normally". I've owned this scooter for several years and its never done this before, so I was wondering what could have caused it and if there is a possible clutch problem in the making.
Any thoughts?
Steve
Recently rode to the Isle of Wight and back (400 miles) with absolutely no problems. Due to holidays, the scooter has been stored in the garage since. Last night I started it up to go to a club meet and when I put it in gear it lurched forward and stalled, even with the clutch pulled in. After 3 or 4 times of doing this it settled down and behaved "normally". I've owned this scooter for several years and its never done this before, so I was wondering what could have caused it and if there is a possible clutch problem in the making.
Any thoughts?
Steve