particles falling through blocks?

i cant understand why this particle is falling through blocks instead of stopping on top of them?

fyi Precipitation extends EntityFX

public class DWRainFX extends Precipitation

{

    private static final String __OBFID = "CL_00000934";

    public DWRainFX(World par1World, double par2, double par4, double par6)

    {

        super(par1World, par2, par4, par6, 0.0D, 0.0D, 0.0D);

        this.motionX *= 0.30000001192092896D;

        this.motionY = (double)((float)Math.random() * 0.2F + 0.1F);

        this.motionZ *= 0.30000001192092896D;

        this.particleRed = 1.0F;

        this.particleGreen = 1.0F;

        this.particleBlue = 1.0F;

        this.setSize(0.01F, 0.01F);

        this.particleGravity = 0.06F;

        this.particleMaxAge = 35/*(int)(8.0D / (Math.random() * 0.8D + 0.2D))*/;

    }

    /**

    * Called to update the entity's position/logic.

    */

    public void onUpdate()

    {

        this.prevPosX = this.posX;

        this.prevPosY = this.posY;

        this.prevPosZ = this.posZ;

        this.motionY -= (double)this.particleGravity;

        this.moveEntity(this.motionX, this.motionY, this.motionZ);

        this.motionX *= 0.9800000190734863D;

        this.motionY *= 0.9800000190734863D;

        this.motionZ *= 0.9800000190734863D;

        if (this.particleMaxAge-- <= 0)

        {

            this.setDead();

        }

        if (this.onGround)

        {

          // this.worldObj.set

        if (Math.random() < 0.5D)

            {

                this.setDead();

            }

            this.motionX *= 0.699999988079071D;

            this.motionZ *= 0.699999988079071D;

            //this.motionY = 0.0;

        }

        Material material = this.worldObj.getBlock(MathHelper.floor_double(this.posX), MathHelper.floor_double(this.posY), MathHelper.floor_double(this.posZ)).getMaterial();

        if (material.isLiquid() || material.isSolid())

        {

            double d0 = (double)((float)(MathHelper.floor_double(this.posY) + 1) - BlockLiquid.getLiquidHeightPercent(this.worldObj.getBlockMetadata(MathHelper.floor_double(this.posX), MathHelper.floor_double(this.posY), MathHelper.floor_double(this.posZ))));

            if (this.posY < d0)

            {

                this.setDead();

            }

        }

    }

    public int getID(){

    return 1;

    }

    public String getName(){

    return "rain";

    }

}