OpenBSD 3.7-current reads from atapi cdrom drive without end

[Stefan Sonnenberg-Carstens <ssc_(_at_)_coolspot_(_dot_)_de>]

Trying something like

dd if=/dev/cd0a of=image.iso

results in a image file which grows forever.
dd does not recognise the end of the cd-rom.
Mount and df show correct sizes of the cd-rom,
about 450 megs.
It happens with *all* cd9660 fs based cd-roms.

Stefan Sonnenberg-Carstens