ucom/uplcom/tty/snoop panic on current

This is what i experience with -CURRENT as of few hours.
(never tried this before, probably it's not something new)

right after boot i attach uplcom based ucom device.
then on one tty i do :

[root_at_phobos ~]# cu -l /dev/ttyU0

and on second tty :

[root_at_phobos ~]# watch /dev/ttyU0

Then when i'm back on the first tty under 'cu', the first key i press it
gives me this :
(i hope there are no errors, as i wrote this by hand)

Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x1c
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xc07d9780
stack pointer           = 0x10:0xe6867a78
frame pointer           = 0x10:0xe6867a88
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 534 (cu)
[thread 100066]
Stopped at     ucomstart+0xb8: movl     0x1c(%eax),%edx
db> trace
ucomstart(c1a99400) at ucomstart+0xb8
ttstart(c1a99400) at ttstart+0x16
ttwrite(c1a99400,e6867b64,30001,0,e6867b64) at ttwrite+0x46c
snplwrite(c1a99400,e6867c88,30001) at snplwrite+0x1cd
ttywrite(c1ff0100,e6867c88,30001,1,e6867c88) at ttywrite+0x2f
spec_write(e6867c14,e6867c60,c056a3e4,e6867c14,30001) at spec_write+0x125
spec_vnoperate(e6867c14) at spec_vnoperate+0x13
vn_write(c1d832a8,e6867c88,c1e2f580,0,c1da24e0) at vn_write+0x1dc
dofilewrite(c1da24e0,c1d832a8,3,bfbfed1b,1) at dofilewrite+0xa8
write(c1da24e0,e6867d14,3,1,202) at write+0x39
syscall(2f,2f,2f,3,bfbfed1b) at syscall+0x213
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (4, FreeBSD ELF32, write), eip = 0x280d4c8f, esp = 0xbfbfeccc,
ebp = 0xbfbfecf8 ---
db>

i'll be glad to provide more info/testing if needed.

--niki