kern/45707: call ddb_vgapost stopped working

[Thomas Klausner <wiz%NetBSD.org@localhost>]

>Number:         45707
>Category:       kern
>Synopsis:       call ddb_vgapost stopped working
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Dec 11 12:00:01 +0000 2011
>Originator:     Thomas Klausner
>Release:        NetBSD 5.99.58
>Organization:
Curiosity is the very basis of education and if you tell me that 
curiosity killed the cat, I say only that the cat died nobly.
- Arnold Edinborough
>Environment:
        
        
System: NetBSD yt.nih.at 5.99.58 NetBSD 5.99.58 (YT) #37: Tue Dec 6 00:14:47 
CET 2011 wiz%yt.nih.at@localhost:/archive/cvs/src/sys/arch/amd64/compile/obj/YT 
amd64
Architecture: x86_64
Machine: amd64
>Description:
My /etc/sysctl.conf contains:
ddb.commandonenter=call ddb_vgapost;bt
this worked for some time, but in the last months it stopped working.
When a panic occurs while the console is in X, it _is_ switched back to text
mode, but all that's displayed is a blinking cursor in the upper left corner.
Aleksej Saushev confirmed that he saw the same problem in
http://mail-index.netbsd.org/current-users/2011/11/23/msg018353.html

Possibly relevant part of dmesg:
# grep -e radeon -e wsdispla  -e vga /var/run/dmesg.boot
vga0 at pci4 dev 0 function 0: ATI Technologies Radeon HD4650 (rev. 0x00)
wsdisplay0 at vga0 kbdmux 1: console (80x25, vt100 emulation)
wsmux1: connecting to wsdisplay0
radeondrm0 at vga0: ATI Radeon HD 4650
radeondrm0: Initialized radeon 1.29.0 20080613
wsdisplay0: screen 1 added (80x25, vt100 emulation)
wsdisplay0: screen 2 added (80x25, vt100 emulation)
wsdisplay0: screen 3 added (80x25, vt100 emulation)
wsdisplay0: screen 4 added (80x25, vt100 emulation)
wskbd0 at ukbd0: console keyboard, using wsdisplay0

>How-To-Repeat:
See above. 
>Fix:
Not provided.

>Unformatted: