Stefan Monnier <monnier@IRO.UMontreal.CA> writes:

> I tried:
>
>   src/emacs -Q src/xdisp.c -l .../nlinum.el -f nlinum-mode
>
> and then moved about in the buffer, but I didn't notice any problem.

Try this with the attached file:

src/emacs -nw -Q foo.el

M-x linum-mode    (you may notice the problem already here)
M-x goto-line 10
C-o

The numbers in the margin get messed up.  I haven't figured out a
consistent way to screw up the motion commands yet.