Bug in LWJGL?

Newbie & Debugging Questions
#1

Okay, so I’m trying to get the angle of two quaternions, and it almost works perfectly, but then it jumps from:

evec angle: 237.44999653311922
evec angle: 119.60001380112993

Can someone tell me how to work past this bug? This is the code to make the bug show up:

FloatBuffer fb = BufferUtils.createFloatBuffer(16);

            // get the current modelview matrix
            GL11.glGetFloat(GL11.GL_MODELVIEW_MATRIX, fb);
            Matrix4f mvm = new Matrix4f();
            mvm.load(fb);


            Quaternion qmv2 = new Quaternion();
            Matrix4f imvm = new Matrix4f();
            Matrix4f.invert(mvm, imvm);
            qmv2.setFromMatrix(imvm);
            qmv2.normalise();

            Matrix3f nil = new Matrix3f();
            nil.setIdentity();
            Quaternion qnil = new Quaternion();
            qnil.setFromMatrix(nil);
            qnil.normalise();

            float radAngle = (float) (2.0 * Math.acos(Quaternion.dot(qmv2, qnil)));

                System.out.println("evec angle: " + Math.toDegrees(radAngle));

Also if I call fb.flip() after glGetFloatv(), but before mvm.load(fb) I get this error:

Exception in thread "main" java.nio.BufferUnderflowException
	at java.nio.Buffer.nextGetIndex(Unknown Source)
	at java.nio.DirectFloatBufferU.get(Unknown Source)
	at org.lwjgl.util.vector.Matrix4f.load(Matrix4f.java:187)
	at NeroEdge.renderGL(NeroEdge.java:424)
	at NeroEdge.run(NeroEdge.java:101)
	at NeroEdge.main(NeroEdge.java:855)
#2

OpenGL commands do not change buffer counters (index, mark, e.t.c), so you don’t have to flip after calling one.

#3

Thought so.