kern/46243: i386: scrollback buffer dissappears and is not consistent

[akosela%andykosela.com@localhost]

>Number:         46243
>Category:       kern
>Synopsis:       i386: scrollback buffer dissappears and is not consistent
>Confidential:   no
>Severity:       non-critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Mar 22 10:25:00 +0000 2012
>Originator:     Andy Kosela
>Release:        NetBSD 5.1.2
>Organization:
>Environment:
NetBSD zoltar.lan 5.1.2 NetBSD 5.1.2 (ZOLTAR) #0: Thu Mar 22 11:08:17 CET 2012  
root%zoltar.lan@localhost:/usr/src/sys/arch/i386/compile/ZOLTAR i386
>Description:
Custom kernel compiled -- GENERIC with added:

options WSDISPLAY_SCROLLBACK_LINES=200

Platform: i386
Scrollback in all virtual consoles behaves very strange.  It starts with 200 
lines of scrollback buffer, then after issuing a few commands at the prompt 
seems to get smaller and provides only 50-75 lines of scrollback buffer.  When 
changing virtual console to the next one it seems to dissappear entirely.

This bug is also easily reproducible on 6.0-BETA.
>How-To-Repeat:

>Fix: