...or it was improperly set the last time...
BTW: most people frown on using the camshaft to rotate the engine (with the belt on)... I suppose it's OK to do before you replace the belt, as you'll be replacing the tensioner, but with the new components in place, it's advised to rotate the engine using a 12-point 19-mm socket on the center crankshaft pulley bolt... (rotating clockwise only!!)
Yuri