Love2D : Problem rotating image in a SpriteBatch

I'm working on a falling blocks type of game with triangular pieces. I'm using a SpriteBatch to accumulate and remember the pieces and their locations.

The problem is that when I rotate a scaled Image of the triangle, I get unexpected results, that is the origin of the sprite rotation is wrong -- but if I rotate a full-size image (no scaling) it works fine. The sprite should rotate from the center of the image (x + xScale * imgWidth / 2) and (y + yScale * imgWidth / 2). When xScale and yScale == 1, everything is fine. But as soon as it scales down to a fraction of the original size, the origin seemingly freaks out to weird sizes. Here's some code to inspect:

function love.load()
    img = love.graphics.newImage("triangle.png")
    sb = love.graphics.newSpriteBatch(img, 1024)
    imgWidth = img:getWidth()
    imgHeight = img:getHeight()
    x = 250
    y = 250
    xScale = 0.4
    yScale = 0.4
    xOrig = (xScale * imgWidth / 2)
    yOrig = (yScale * imgHeight / 2)
    angleDirection = 0
    id = sb:add(x, y, math.rad(angleDirection), xScale, yScale, xOrig, yOrig, 0, 0)
end

function love.update(dt)
    if love.keyboard.isDown(" ") then
        angleDirection = angleDirection + 180
        if angleDirection >= 360 then
            angleDirection = 0
        end
    end
    sb:set(id, x, y, math.rad(angleDirection), xScale, yScale, xOrig, yOrig, 0, 0)
end

function love.draw()
    love.graphics.draw(sb)
end

Now, to see the problem in action, run the preceding code. Change the xScale and yScale to a 1 to see the rotation work properly. Thanks in advance for any suggestions you have.