bug#12927: 24.2; global-hl-line-mode and "scroll-conservatively=1000" take jump up-down the text when hold DOWN key (in *info* buffer).

[Oleksandr Gavenko]

As usual:

  $ emacs -Q

then:

  (setq scroll-conservatively 1000)
  (global-hl-line-mode 1)

and "C-h i". I press and hold DOWN key. After some time cursor reach end of
frame and then text scroll up but sometimes it seems as text jump down! And I
get fill that text moving have jerks.

I make record of this actions:

  $ cvlc screen:// --screen-fps=60 --no-sout-audio --sout 
"#transcode{venc=x264,quality:100,scale=1,fps=60}:duplicate{dst=std{access=file,mux=mp4,dst=desktop.ogg}}}"

To download (less then 1 MiB) this record:

  $ wget http://gavenkoa.users.sf.net/desktop.ogg

If slow down speed in video viewer you can see that sometimes point jump over
1 line (so move to the second line, without visiting next), so it lost smooth
scrolling. But on video it look better then in real screen. And I can't
describe it better as non naive English speaker...

Without (global-hl-line-mode 1) text only scroll up as desired (smooth,
without abrupt jumps).

In GNU Emacs 24.2.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.10)
 of 2012-09-09 on trouble, modified by Debian

-- 
Best regards!