Read-only mount attribute not remembered across reboot

[thebuck]

R1beta4tc0, automount settings:

• automatic mount: (1st) do not auto-mount
• mount at boot: (2nd) mount previously mounted disks

But my previously read-only mounted EXT filesystem is mounted read-write on next boot.

At the same time another previously not-mounted EXT is correctly not mounted.

Haiku booted from a MBR partitioned thumbdrive (with handcrafted MBR, BeFS partition extracted from iso, dd'ed to partition, makebootabletiny).
Set failsafe video in bootmenu.
x86_64.
MBR partition table where the EXTs reside.
Traditional BIOS.

I do not know of any working hrev.

Increases chance of data loss, so setting to high priority. Guessed component.