I was riding home last night and I was shifting up through the gears, and I had just changed into 5th and gave it a few revs when the engine roared as if I was revving with the clutch in. I stop revving and pull the clutch in, release and its in gear. Yesterday was the first time it happened but I can't remember if I gave the gear pedal a half nudge if you know what I mean. Is it normal for a bike to slip gears or is it the sign of a problem? I recently had the clutch cable replaced so I am hoping that its ok.