It occurred to me that Aleksey Cheusov wrote in gmane.os.netbsd.documentation:
> There is a bug in section "4.7. System time"
> of NetBSD.
> In case a system time is set to local time,
> it is necessary to add
>
> rtclocaltime=YES
>
> to /etc/rc.conf
> and to set /etc/localtime properly.

The guide text is outdated - but still valid. All rtclocaltime does is
adjusting kern.rtc_offset.