Why this eval command for mode line makes scroll-conservatively *not* work right anymore? (CLASHING!!!)

[Christian Seberino]

For various reasons I used an eval command in mode-line config to add
1 to column number:

; Modeline

   (setq-default default-mode-line-format
      (list ""
            'mode-line-buffer-identification
            "     "
            (system-name)
            "     "
            "Line %l Column "
            '(:eval (format "%d" (1+ (current-column))))))
   (add-hook            'post-command-hook        
      (lambda () (force-mode-line-update)))
   (setq-default        line-number-display-limit 10000000)
   (set-face-background 'modeline                 "red"   )
   (set-face-foreground 'modeline                 "black" )

I also set scroll behavior to only move by 1 line at a time instead of
jerking cursor to middle of the screen all the time...

     (setq-default        scroll-conservatively  1000              )


The modeline magic above makes this scroll line be IGNORED?!?!?

Why do they clash and how disentangle these guys so they BOTH work?

thanks in advance,

Chris