Friction slowing down my player even when cero

Hi, I've been able to put a so so Mario like
platform game. I can make my player walk over the
tiles but when he is moving sometimes he loses speed
and stops even when I'm pressing the left key:

I'm using:

playerMap.bindCmd(keyboard, "left", "circleGuyLeft();", "circleGuyLeftStop();");

and

function circleGuyLeft()
{
	$player.playAnimation(circleGuyWalkLeft);   
	$player.setLinearVelocityX (-45);
}

function circleGuyLeftStop()
{
	if ($player.getLinearVelocityX() < 0)
	{
		$player.setLinearVelocityX (0);
		$player.playAnimation(circleGuyStandLeft);
	}
}

as materials I set the friction to CERO,

// --------------------------------------------------------------------
// Immovable Collision Material.
// --------------------------------------------------------------------
datablock fxCollisionMaterialDatablock2D(immovableMaterial)
{
	friction = 0.0;
	restitution = 0.0;
	relaxation = 0.5;
	density = 0.01;
	forceScale = 0;
	damping = 0.0;
};
// --------------------------------------------------------------------
// Standard Collision Material.
// --------------------------------------------------------------------
datablock fxCollisionMaterialDatablock2D(standardMaterial)
{
	friction = 0.0;  // <<< CERO!
	restitution = 0.0;
	relaxation = 0.5;
	density = 0.01;
	forceScale = 1;
	damping = 0.0;
};

I don't understand why the player is still slowing down
Can someone give advice about this?

It seems this problem only happens when the movement is in
the left direction.