PIL rendering strange artifacts in text

Question

I'm trying to use PIL to render some images of characters. For some reason, about 1% of the characters rendered have strange artifacts like those shown below. The second one is supposed to be a "v".

This is a consistent phenomenon. For the same font, character and size, the artifacts always look the same. This happens with a lot of different fonts. The example above is 20 pt "aakar-medium". The code used to perform this rendering is below.

def renderChar(char, font, size, dest):
    to_render = char
    txt_font  = ImageFont.truetype(font, size=size)
    dims      = txt_font.getsize(to_render)
    dims      = (dims[0] + 4, dims[1] + 4)
    image     = Image.new("RGBA", dims, (255, 255, 255))
    draw      = ImageDraw.Draw(image)

    draw.text((2, 2), to_render, (0, 0, 0), font=txt_font)
    image.save(dest)

As you can see, I've also added some padding because of another issue. The characters are getting cut off in some cases. That appears to be solved in another question on StackOverflow. While I'd appreciate help with that too, it isn't my primary concern. I'm saving these images as *.bmp files. I've also tried *.png and *.jpg, both of which have more severe artifacts. I'm assuming that some of this is due to compression. I've also tried using an image in "RGB" mode (rather than "RGBA"). This made no difference.

Edit: At the suggestion of martineau, I have posted this bug to https://github.com/python-pillow/Pillow/issues/4645