I have run into this issue too. Racking on top of the sugar may not be enough to mix the sugar in. On a recent batch, the first 6-12 bottles got too much sugar and are overcarbed volcanoes now. the later bottles were lightly carbed. The moral of the story is to stir the beer gently to ensure the sugar gets mixed evenly in your bottling bucket.
Also, many will tell you that 2 weeks is really the minimum. High grav beers can take much longer.