When scroll-step is 1 and if first displayed line overlapped and you go up one line or fisrt
non-displayed line at bottom overlapped and you go down one line moving cause displaing engine
redisplay windows content and center point as done by 'C-l'. So take it greater.
Set margin only for desired modes! Do not frustrate calendar any more.
Also set margin to 4 lines as continent see more next strings.
My grouped lists of modes was placed at top.
Do not change default-major-mode from fundamental-mode.
When it was set to text-mode text-mode-hook have affect on calendar mode and
when margin was set in hook it also set in calendar.