Scale takes already scaled and interpolated image and scale it again, loosing quality.

[MarioMey]

Steps to reproduce and understand this issue

• Configure scene resolution to 720x1280 (portrait proportions)
• Import a 1280x720 image/video
  -- (Image/video is scaled automatically to fit in portrait shape)
• Apply VSE Transform Tool by pressing "S".
• Chage its scale to original proportion by pressing "Alt-S".
• Image is like:
  

Steps to avoid this quality loss

• Don't apply VSE Transform Tool. Instead of that, check "Offset" in "Transform" / "Adjust" panel.
• Change "Position X" to -440.
• Image is: