The "quality" parameter seems to be ignored (in templates)

According to the docs (https://www.buzzingpixel.com/software/ansel-ee/documentation/templating#onTheFlyCroppingAndResizing), I should be able to change the quality on the fly.

<img src="{img:url:resize quality='99'}">
<img src="{img:url:resize quality='10'}">

results in 2 different files with the exact same size. It doesn't matter if I also crop or scale_up. Width, Height, Crop all seem to work as intended.

The same seems to be true for the quality settings of the field itself. Changing quality from 1 to 100 results in the same filesize when uploading the same image again.

Edit: Tested with a new channel and a new field: Changing the field setting from 1 to 100 does work when an image is uploaded.

But trying to change the quality in the template:

img:url:resize quality="11"
img:url:resize quality="22"
img:url:resize quality="88"
img:url:resize quality="99"

will generate 4 images in _ansel_image_cache, but the quality / filesize does not change, they are all the same.

What am I doing wrong?

Also: It seems changing the quality and resizing is applied to the image that was uploaded and then saved again with the (initial) settings of the field itself. Yet the original image is also kept. Shouldn't resizing and changing quality be applied to the original image rather than the already modified image? Setting quality=100 in a template on an image that was reduced to quality = 50 by the field settings when uploaded seems pointless. If not, why do we keep the original image?

"[x] Keep original image" seems like a good option to prevent keeping files we don't actually need?