Emacs: 26.0.90

OS: debian 8.0 x86_64

1. start emacs with -Q arg

2. eval the followng lisp code:

(progn

(set-frame-font "Monospace:size=18")

(set-face-attribute 'mode-line nil :font "Monospace:size=18" :height 0.9)

(setq scroll-margin 2

scroll-conservatively 0)

(setq-default header-line-format mode-line-format))

3. open a test file with lines more than window-height

4. go to end of buffer

5. eval this line: (scroll-down 100)

6. Now the margin seems not be 2. If I press M-x, emacs scrolls.

PS: The next-line command doesn’t trigger the problem.