install/54788: Installation of system breaks on bootcode setting

[guest01%uo.com@localhost]

>Number:         54788
>Category:       install
>Synopsis:       Installation of system breaks on bootcode setting
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Dec 19 15:20:00 +0000 2019
>Originator:     guest01
>Release:        NetBSD 9.0 RC1
>Organization:
>Environment:
amd64
>Description:
When I install NetBSD 9.0 RC1 on computer with NetBSD 8.0 RC1 and I select bootcode option the instalation is broken with message:
"assertion "false" failed: file "usr/src/usr.sbin/sysinst/arch/amd64
[1] Abort trap (core dumped) ${cmd}
To return to the installer, quit this shell by typing 'exit' or ^D
>How-To-Repeat:
Try to install NetBSD 9.0 RC1 on partition with NetBSD 8.0.
Boot computer with an image based on NetBSD-9.0_RC1-amd64-install.img.gz.
Start installation procedure.
When you get bootcode option screen you will get message:
The bootcode in Master Boot Record does not appear to be valid.
Do you want to install the NetBSD bootcode ?
When you choose any option you will get error message.

>Fix: