Severe artifact when interpolating between dual quaternions - matrix

Question

I'm having trouble with my implementation of dual quaternion skinning. I'm still learning about the subject, so for the moment I'm converting from the bone matrix to a dual quaternion CPU side, and back to a matrix in the shader.
The conversion does apparently work correctly for single bones, but if I try to linearly blend between dual quaternions, I get this artifact:
http://imagizer.imageshack.us/a/img838/8671/nun.gif
I don't know what's causing this. Maybe it's related to how I normalize the dual quaternion, maybe it's in how I convert from dual quat to matrix. I've tried searching for actual dual quaternion code, but all I find is a bunch of hard to read mathematical definitions.
I am including pieces of the shader code, as I'm pretty sure that's where the problem is. Hopefully somebody proficient in quaternion math can look through it!
Blending the dual quaternions. Boneweight2 = (1.0 - boneweight1), so they'll always sum up to 1.
vec4 blendReal = boneReal[bone1] * boneWeight1 + boneReal[bone2] * boneWeight2;
vec4 blendDual = boneDual[bone1] * boneWeight1 + boneDual[bone2] * boneWeight2;
float blend_norm_real = length(blendReal);
blendReal /= blend_norm_real;
blendDual /= blend_norm_real;
Create matrix from dual quaternion:
mat4 MatFromDualQuat(vec4 rq, vec4 dq)
{
//Source: Section 3.4 http://www.seas.upenn.edu/~ladislav/papers/sdq-i3d07/sdq-i3d07.pdf
//rq = real quaternion
//dq = dual quaternion
mat4 M;
M[0][0] = 1.0 - 2.0 * (rq.y * rq.y + rq.z * rq.z); //
M[1][0] = 2.0 * (rq.x * rq.y + rq.w * rq.z);//
M[2][0] = 2.0 * (rq.w * rq.y - rq.x * rq.z);//
M[3][0] = 0.0;
M[0][1] = 2.0 * (rq.x * rq.y - rq.w * rq.z);
M[1][1] = 1.0 - 2.0 * (rq.x * rq.x + rq.z * rq.z);
M[2][1] = 2.0 * (rq.y * rq.z + rq.w * rq.x);
M[3][1] = 0.0;
M[0][2] = - 2.0 * (rq.x * rq.z + rq.w * rq.y);
M[1][2] = 2.0 * (rq.y * rq.z - rq.w * rq.x);
M[2][2] = 1.0 - 2.0 * (rq.x * rq.x + rq.y * rq.y);
M[3][2] = 0.0;
M[0][3] = 2.0 * (-dq.w * rq.x + dq.x * rq.w + dq.z * rq.y - dq.y * rq.z);
M[1][3] = 2.0 * (-dq.w * rq.y + dq.y * rq.w + dq.x * rq.z - dq.z * rq.x);
M[2][3] = 2.0 * (-dq.w * rq.z + dq.z * rq.w + dq.y * rq.x - dq.x * rq.y);
M[3][3] = 1.0;
return M;
}
And then I multiply that with the bind pose vertex position.