OpenGl/TF: Help with results i can't explain and centering geometry

<jittershader name="TFFlowfield">
	<description>Basic Transform Feedback Locomotion</description>
	<param name="position" type="vec3" state="POSITION" />
	<param name="velocity" type="vec3" state="NORMAL" />
	<param name="speed" type="float" default="0.005" />
	<param name="theta" type="float" default="0.0" />
	
	<param name="randomTex" type="int" default="0" />
	
	<language name="glsl" version="1.5">
		<bind param="position" program="vp" />
		<bind param="velocity" program="vp" />
		<bind param="speed" program="vp" />
		<bind param="theta" program="vp" />
		
		<bind param="randomTex" program="vp" />
		
		<program name="vp" type="vertex">
<![CDATA[
#version 330 core
uniform float speed;
uniform float theta;
in vec3 position;
in vec3 velocity;

out vec3 Position1;
out vec3 Velocity1;

const float PI = 3.1415926535897932384626433832795;

uniform sampler2DRect randomTex;

void main() {
	
	vec2 texLookup = vec2(position.x * 99.0, position.y * 99.0);
	float theta = texture(randomTex, texLookup).x;
	
	Position1.x = mod(1.0 + (position.x + (cos(theta * (PI * 2)) * speed)), 1.0);
	Position1.y = mod(1.0 + (position.y + (sin(theta * (PI * 2)) * speed)), 1.0);
	Position1.z = 0.0;
	
	Velocity1.x += 0.00001;
	Velocity1.y = velocity.y;
	Velocity1.z = velocity.z;
	
	if(Velocity1.x > 1.0) 
		{
			Position1 = vec3(0.5, 0.5, 0.0);

			//Position1 = vec3(velocity.y, velocity.z, 0.0); // Why doesn't this line work but line 48 does?
				
			
			//Position1.x = velocity.y; //And why doesn't this work when it does on line 38?
			//Position1.y = velocity.z;
			//Position1.z = 0.0;
			
			Velocity1.x = 0.0;
		}
	
}

]]>
		</program>
		<program name="fp" type="fragment"  >
		<![CDATA[
#version 330 core
void main() 
{
}
		]]>
		</program>
	</language>
</jittershader>