First random number after setSeed in Java always similar

To give some context, I have been writing a basic Perlin noise implementation in Java, and when it came to implementing seeding, I had encountered a bug that I couldn't explain.

In order to generate the same random weight vectors each time for the same seed no matter which set of coordinates' noise level is queried and in what order, I generated a new seed (newSeed), based on a combination of the original seed and the coordinates of the weight vector, and used this as the seed for the randomization of the weight vector by running:

rnd.setSeed(newSeed);
weight = new NVector(2);
weight.setElement(0, rnd.nextDouble() * 2 - 1);
weight.setElement(1, rnd.nextDouble() * 2 - 1);
weight.normalize()

Where NVector is a self-made class for vector mathematics.

However, when run, the program generated very bad noise:

After some digging, I found that the first element of each vector was very similar (and so the first nextDouble() call after each setSeed() call) resulting in the first element of every vector in the vector grid being similar.

This can be proved by running:

long seed = Long.valueOf(args[0]);
int loops = Integer.valueOf(args[1]);
double avgFirst = 0.0, avgSecond = 0.0, avgThird = 0.0;
double lastfirst = 0.0, lastSecond = 0.0, lastThird = 0.0;
for(int i = 0; i<loops; i++)
{
    ran.setSeed(seed + i);
    double first = ran.nextDouble();
    double second = ran.nextDouble();
    double third = ran.nextDouble();
    avgFirst += Math.abs(first - lastfirst);
    avgSecond += Math.abs(second - lastSecond);
    avgThird += Math.abs(third - lastThird);
    lastfirst = first;
    lastSecond = second;
    lastThird = third;
}
System.out.println("Average first difference.: " + avgFirst/loops);
System.out.println("Average second Difference: " + avgSecond/loops);
System.out.println("Average third Difference.: " + avgSecond/loops);

Which finds the average difference between the first, second and third random numbers generated after a setSeed() method has been called over a range of seeds as specified by the program's arguments; which for me returned these results:

C:\java Test 462454356345 10000
Average first difference.: 7.44638117976783E-4
Average second Difference: 0.34131692827329957
Average third Difference.: 0.34131692827329957

C:\java Test 46245445 10000
Average first difference.: 0.0017196011123287126
Average second Difference: 0.3416750057190849
Average third Difference.: 0.3416750057190849

C:\java Test 1 10000
Average first difference.: 0.0021601598225344998
Average second Difference: 0.3409914232342002
Average third Difference.: 0.3409914232342002

Here you can see that the first average difference is significantly smaller than the rest, and seemingly decreasing with higher seeds.

As such, by adding a simple dummy call to nextDouble() before setting the weight vector, I was able to fix my perlin noise implementation:

rnd.setSeed(newSeed);
rnd.nextDouble();
weight.setElement(0, rnd.nextDouble() * 2 - 1);
weight.setElement(1, rnd.nextDouble() * 2 - 1);

Resulting in:

I would like to know why this bad variation in the first call to nextDouble() (I have not checked other types of randomness) occurs and/or to alert people to this issue.

Of course, it could just be an implementation error on my behalf, which I would be greatful if it were pointed out to me.