when you create bookmarks (just put black arrow or square in the corner without information about how to add bookmarks and without invert)
lock reader (return back to the previous option or put down a symbol of key and let the content displayed or let the reader decide the option in settings if the content is visible or not)
i prefer lock by touching some reserved place with symbol otherwise pressing on/off button, which is unable to press with one hand reading
maybe this reserved place could by active also for unlocking
startup reader (screen inverts twice without reason - if i have set booting with showing reading book I can start read immediately abter pushing on/off button and system can load on background without inverts)
conclusion - too much gratuitous inverts for only reader bother and reduce batter life
thanks for solving
PB622 is great reader