Weird problem with advect program in fluid simulator

Question

I implemented 2d fluid simulator. Solver runs entirely on GPU. All works fine... on my work PC. But on home PC I have some awful glitches, and I can`t understand how to fix them. Empirically I discovered that problem is localized somewhere in advect program. This is very strange cause at work I have integrated video, and at home — NVIDIA GeForce 9800 GT. Here is the GLSL source of advect program (some lines were dropped for clearness):

#version 130

out vec3 value;

uniform sampler2D q;
uniform sampler2D velocity;
uniform float dt;
uniform float inverseSize;

void main()
{   
  vec2 p = gl_FragCoord.xy * inverseSize; 

  vec2 np = p - dt * texture(velocity, p).xy;

  value = texture(q, np).xyz;
}

And some screenshots.

Work PC:

Home PC:

Answer 1

Per the OP's response, substituting

vec2 np = p - dt * texture(velocity, p).xy;

for

vec2 np = p - dt * vec2(0.01);

solved the problem. The field and density moves smoothly in the (0.01, 0.01) direction.