cu hanging on zstty (/dev/cuab)

Hi,

on my SS5, and also on my SPARCbook 3 I have zs and zstty, but trying to connect
to a remote serial console on such ports doesn't seem to work.

It doesn't even tell me its getting connected:
cu -l /dev/cuab -s 9600

cu seems to hang in cu.c here:
line_fd = open(line, O_RDWR);

I installed uucp from ports, and tried that cu there, and there at least it tells me
it gets connected, but when I enter a character, I get an I/O error.

# /usr/local/bin/cu -l /dev/cuab -s 9600        
Connected.
/usr/local/bin/cu: write: Input/output error

ktrace told me that the I/O error comes from a write on FD3, 
which apparently is the cuab device.

The serial console on both machines work, when I connect from 
another host to both, the SS5 or the notebook, then I get the
serial console.

Sebastian

OpenBSD 5.3-current (GENERIC) #21: Sat Mar 23 17:23:36 MDT 2013
    [email protected]:/usr/src/sys/arch/sparc/compile/GENERIC
real mem = 200933376 (191MB)
avail mem = 192954368 (184MB)
mainbus0 at root: SUNW,SPARCstation-5
cpu0 at mainbus0: MB86907 @ 170 MHz, on-chip FPU
cpu0: 16K instruction (32 b/l), 16K data (32 b/l), 512K external (32 b/l) DVMA coherent cache enabled
obio0 at mainbus0
clock0 at obio0 addr 0x71200000: mk48t08 (eeprom)
timer0 at obio0 addr 0x71d00000: delay constant 82, frequency 2000000 Hz
zs0 at obio0 addr 0x71100000 pri 12, softpri 6
zstty0 at zs0 channel 0: console
zstty1 at zs0 channel 1
zs1 at obio0 addr 0x71000000 pri 12, softpri 6
zskbd0 at zs1 channel 0: no keyboard
zsms0 at zs1 channel 1
wsmouse0 at zsms0 mux 0
slavioconfig at obio0 addr 0x71800000 not configured
auxreg0 at obio0 addr 0x71900000
power0 at obio0 addr 0x71910000
fdc0 at obio0 addr 0x71400000 pri 11, softpri 4: chip 82077
iommu0 at mainbus0 addr 0x10000000: version 0x5/0x0, page-size 4096, range 64MB
sbus0 at iommu0: 21.250 MHz
dma0 at sbus0 slot 5 offset 0x8400000: rev 2
esp0 at dma0 offset 0x8800000 pri 4: ESP200, 40MHz
scsibus0 at esp0: 8 targets, initiator 7
cd0 at scsibus0 targ 2 lun 0: <MATSHITA, CD-ROM CR-504, ST23> SCSI2 5/cdrom removable
sd0 at scsibus0 targ 3 lun 0: <IBM, DCAS32160SUN2.1G, S60B> SCSI2 0/direct fixed serial.IBM_DCAS32160SUN2.1GF2583160_
sd0: 2063MB, 512 bytes/sector, 4226725 sectors
bpp0 at sbus0 slot 5 offset 0xc800000: DMA2
ledma0 at sbus0 slot 5 offset 0x8400010: rev 2
le0 at ledma0 offset 0x8c00000 pri 6: address 08:00:20:89:d9:b5
le0: 16 receive buffers, 4 transmit buffers
audiocs0 at sbus0 slot 4 offset 0xc000000 pri 9
audio0 at audiocs0
"power-management" at sbus0 slot 4 offset 0xa000000 not configured
cgsix0 at sbus0 slot 3 offset 0x0 pri 9: SUNW,501-2325, 1152x900, rev 11
wsdisplay0 at cgsix0 mux 1
wsdisplay0: screen 0 added (std, sun emulation)
vscsi0 at root
scsibus1 at vscsi0: 256 targets
softraid0 at root
scsibus2 at softraid0: 256 targets
bootpath: /iommu@0,10000000/sbus@0,10001000/espdma@5,8400000/esp@5,8800000/sd@3,0
root on sd0a (1096ee405a923d3e.a) swap on sd0b dump on sd0b