Apple Preview is perfect tool for pdf manipulation: adding, removing and rearranging pages. I've been using Preview this way for about 10 years without fail. Recently I've noticed that pdf-s from Scannable app change colour (turn into red, yellow, purple, etc) if pages in it are rearranged for example (or merged into another pdf). I can not replicate this issue with pdf-s from other sources.
Attached is a screenshot of a three-page scannable scan, where two pages (green and purple) are rearranged, one (white) is in its original location. All three should be white.
What can be the reason behind this?