[marais]

It seems it was just a setting. In tools preferences I had checked to display half pages in Landscape mode. =
 Display Half Page in Landscape
o Displays half a page in landscape orientation while using the single page
display mode. Pages can be scrolled up and down.  Half-Page Turns In Landscape Mode
o Advances half a page at a time while the single page display mode is active in Landscape Mode. Vertical scrolling is disabled while this mode is active.

- My fault. -
If this hasn't cleared it up of course will get back.