install/54937: "install" flag does not set in sysinst

[i@-.-]

>Number:         54937
>Category:       install
>Synopsis:       "install" flag does not set in sysinst
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 04 23:30:00 +0000 2020
>Originator:     guest01
>Release:        9.0_RC2
>Organization:
-
>Environment:
amd64
>Description:
Almost the same problem to #54787.
This problem occur when you install NetBSD 9.0_RC2 on disk with a partition created in NetBSD 8.0 because sysinst in 9.0_RC2 changes start sector of MBR partition. In my example it changes from 63 to 2048. It happens when you try set install flag of MBR partition.
When you set install flag of MBR partition, the flag is not set but start sector is changed. You must set install flag second time and then it is set.
But in NetBSD 9.0_RC2 (maybe with just one MBR partition ?) setting install flag does not matter. You can install system without setting install flag.
>How-To-Repeat:
First create partitions with NetBSD 8.0.
Boot computer with system installation disk and select:
        1	Install NetBSD
	2	Keyboard type b: US-English
	3	a: Install NetBSD to hard disk
	4	Shall we continue ? b: Yes
	5	On which disk do you want to install NetBSD? a: wd0
	6	a: This is the correct geometry
	7	b: Use the entire disk
	8	Do you want to update the bootcode in the Master Boot
                Record to the latest version of the NetBSD bootcode?
                a: Yes
	9	a: Set sizes of NetBSD partitions
	10	x: Accept partition sizes
	11	x: Partition sizes ok
	12	Please enter a name for your NetBSD disk [wd]:
	13	Shall we continue? b: Yes
	14	Selected bootblock: BIOS console x: Exit
	15	Abandon installation

Next try install NetBSD 9.0_RC2 on prepared disk.
Boot computer with NetBSD 9.0_RC2 installation disk and select:
        1	a: Install NetBSD to hard disk
	2	Shall we continue? b: Yes
	3	On which disk do you want to install NetBSD? a: wd0
	4	a: This is the correct geometry
	5	b: Edit the MBR partition table
	6	   Start(MB)   Size(MB) Flag Kind	Mount   Bootmenu
		           0     152627 a    NetBSD	/
	7	e: install: Yes
	8	x: Partition OK
	9          Start(MB)   Size(MB) Flag Kind	Mount   Bootmenu
		           1     152627 a    NetBSD	/
		Install flag is not set but Start is changed from 0 to 1
>Fix: