Please describe the problem:
It looks like that scale tool ignores interpolation type (at least at downscaling)

Steps to reproduce:
1. Take a sharped photo (to see the difference better) with unique layer
2. Duplicate layer
3. Downscale 1st later using Scale tool and Lanczos 
4. Downscale 2nd layer using Scale tool and Cubic
5. Set 'Difference' as mode of upper layer


Actual results:
No diference: black image

Expected results:
If use Image/Scale, I see the difference: Cubic is more blurred

Does this happen every time?
Yes

Other information:
To be more exact: I downscale the image with size 5443x3598 with scale 66%.