I've come across a problem with the collision detection code in the platformer starter kit for xna.It will send up the impassible flag on the x axis despite being nowhere near a wall in either direction on the x axis, could someone could tell me why this happens ?

Here is the collision method.

  /// <summary>
    /// Detects and resolves all collisions between the player and his neighboring
    /// tiles. When a collision is detected, the player is pushed away along one
    /// axis to prevent overlapping. There is some special logic for the Y axis to
    /// handle platforms which behave differently depending on direction of movement.
    /// </summary>
    private void HandleCollisions()
    {
        // Get the player's bounding rectangle and find neighboring tiles.
        Rectangle bounds = BoundingRectangle;
        int leftTile = (int)Math.Floor((float)bounds.Left / Tile.Width);
        int rightTile = (int)Math.Ceiling(((float)bounds.Right / Tile.Width)) - 1;
        int topTile = (int)Math.Floor((float)bounds.Top / Tile.Height);
        int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / Tile.Height)) - 1;

        // Reset flag to search for ground collision.
        isOnGround = false;

        // For each potentially colliding tile,
        for (int y = topTile; y <= bottomTile; ++y)
        {
            for (int x = leftTile; x <= rightTile; ++x)
            {
                // If this tile is collidable,
                TileCollision collision = Level.GetCollision(x, y);
                if (collision != TileCollision.Passable)
                {
                    // Determine collision depth (with direction) and magnitude.
                    Rectangle tileBounds = Level.GetBounds(x, y);
                    Vector2 depth = RectangleExtensions.GetIntersectionDepth(bounds, tileBounds);
                    if (depth != Vector2.Zero)
                    {
                        float absDepthX = Math.Abs(depth.X);
                        float absDepthY = Math.Abs(depth.Y);

                        // Resolve the collision along the shallow axis.
                        if (absDepthY < absDepthX || collision == TileCollision.Platform)
                        {
                            // If we crossed the top of a tile, we are on the ground.
                            if (previousBottom <= tileBounds.Top)
                                isOnGround = true;

                            // Ignore platforms, unless we are on the ground.
                            if (collision == TileCollision.Impassable || IsOnGround)
                            {
                                // Resolve the collision along the Y axis.
                                Position = new Vector2(Position.X, Position.Y + depth.Y);

                                // Perform further collisions with the new bounds.
                                bounds = BoundingRectangle;
                            }
                        }
                       //This is the section which deals with collision on the x-axis
                        else if (collision == TileCollision.Impassable) // Ignore platforms.
                        {
                            // Resolve the collision along the X axis.
                            Position = new Vector2(Position.X + depth.X, Position.Y);

                            // Perform further collisions with the new bounds.
                            bounds = BoundingRectangle;
                        }
                    }
                }
            }
        }

        // Save the new bounds bottom.
        previousBottom = bounds.Bottom;
    }